Rozprawy doktorskie na temat „Maize yield”

This dissertation describes efforts to move toward the study of soil and the management of yield variability through research that explored and evaluated the potential of some techniques to provide greater understanding and knowledge of an agricultural field, even in situations where there is no prior knowledge of its behavior. The first experiment used a principal components analysis (PCA) in the study of the spatial and temporal variability of maize grain yield. The results of this experiment demonstrated that the 1st and 2nd principal components could be used to identify field zones with different spatial and temporal behaviors. The second experiment applied stochastic and sequential Gaussian simulation techniques to spatially and temporally forecast and model maize productivity. This technique enabled the modeling of spatial uncertainty in maize productivity based on probabilistic maps with different confidence levels. The third experiment examined different fertilization input scenarios based on yield/nutrient inputs ratio and break-even yields to optimize agronomic, economic and environmental support decisions. According to the results, it is possible to reduce agricultural production costs through the differential management of inputs. The outcomes showed that differential management decisions can maximize returns and reduce activity risk without having to implement major changes on the farm; Sumário: Otimização da produtividade e dos fatores de produção no milho de regadio O presente trabalho de investigação, que considerou três estudos, explora e avalia o potencial de alguns modelos no estudo da gestão da variabilidade espacial e temporal da produtividade e dos nutrientes no âmbito da produção de regadio. O primeiro estudo focou a utilização da técnica estatística Análise de Componentes Principais (ACP) no estudo da variabilidade temporal da produtividade da cultura do milho na região do Alto Alentejo. Os resultados desta experiência mostraram que as duas primeiras componentes principais permitem identificar zonas da parcela agrícola com diferente comportamento espacial e ambiental. No segundo estudo avaliou-se o desempenho da simulação sequencial Gaussiana na previsão e modelação da produtividade da cultura do milho. Esta técnica permitiu modelar a incerteza espacial da produtividade com base em mapas de probabilidade com diferentes níveis de confiança. O terceiro estudo avaliou diferentes cenários de fertilização a partir do rácio produtividade/nutrientes e do breakeven da produtividade de forma a otimizar, em termos agronómicos, económicos e ambientais, as tomadas de decisão. De acordo com os resultados obtidos, foi possível obter uma redução substancial dos custos de produção através da sugestão da aplicação diferenciada da fertilização. Os resultados mostraram que é possível reduzir os riscos, quer económicos quer ambientais, da atividade agrícola sem grandes alterações no processo produtivo da exploração agrícola.

Crop simulation models (CSMs) are used to evaluate management and environmental scenarios on crop growth and yields. Two corn (Zea Mays L.) crop growth simulation models, Hybrid-Maize, and CERES-Maize were calibrated and validated under Virginia conditions with the goal of better understanding corn response to variable environmental conditions and decreasing temporal yield variation. Calibration data were generated from small plot studies conducted at five site-years. Main plots were plant density (4.9, 6.2, 7.4, and 8.6 plants m-2); subplots were hybrids of differing relative maturity (RM) [early = Pioneer® Brand â 34B97â (108 day RM); medium = Pioneer® Brand â 33M54â (114 day RM); and late = Pioneer® Brand â 31G66â (118 day RM)]. Model validation was generated from large scale, replicated strip plot trials conducted at various locations across Virginia in 2005 and 2006. Prior to model adjustments based on calibration data, both CSMs under predicted corn grain yield in calibration and validation studies. CERES-Maize grain yield prediction error was consistent across the range of tested plant density while accuracy of Hybrid-Maize varied with plant density. Hybrid-Maize-estimated biomass production was highly accurate. Greater leaf area index (LAI) and biomass production were measured than was predicted by the CERES-Maize CSM. Both CSMs were modified based on calibration data sets and validated. Validation results of the calibrated CSMs showed improved accuracy in simulating planting date and environmental effects on a range of corn hybrids grown throughout Virginia over two years. We expect that both modified models can be used for strategic research and management decisions in mid-Atlantic corn production.
Master of Science

Mestrado em Engenharia Agronómica / Instituto Superior de Agronomia. Universidade de Lisboa
Over the decades, it has been found that agricultural intensification, that is, the increase in production per hectare, is substantially urgent and necessary, justified by the observed and expected population increase and the impossibility of agricultural expansion. One of the methods for achieving this goal is the study and investigation of yield gaps, which may be explained by unfavorable soil and climate conditions, or less adequate input management. Given the socio-economic importance of maize crop in Portugal and the need for case studies that exemplify agricultural intensification methods, this dissertation aims to discover which are the reducing factors that justify the gap between the maximum and actual yields, known as yield gaps, which were analyzed between plots and years, and how large was the yield gap over the 10 years. Through a database of irrigation appropriations, nitrogen applications, sowing dates and climate data, collected over 10 years and provided by Milho Amarelo company, located in the Santarem region, other variables were calculated, such as degree-day accumulation, cultural evapotranspiration and intercepted radiation. These data were analyzed annually according to the whole cycle and according to different phenological phases (vegetative and reproductive). Once all variables were obtained and organized, statistical methods of bivariate and multivariate analysis were performed. The magnitude of yield gap was calculated according to the Approach 2 indicated by FAO 41. The results show that interaction of sowing dates with climatic conditions are in the nature of this deviation, with gap’s magnitude ranging from 5% to 20%, depending on the climatic conditions of the year
N/A

Root-yield-1.06 is a major QTL affecting root system architecture (RSA) and other agronomic traits in maize. The effect of this QTL has been evaluated with the development of near isogenic lines (NILs) differing at the QTL position. The objective of this study was to fine map qroot-yield-1.06 by marker-assisted searching for chromosome recombinants in the QTL interval and concurrent root phenotyping in both controlled and field conditions, through successive generations. Complementary approaches such as QTL meta-analysis and RNA-seq were deployed in order to help prioritizing candidate genes within the QTL target region. Using a selected group of genotypes, field based root analysis by ‘shovelomics’ enabled to accurately collect RSA information of adult maize plants. Shovelomics combined with software-assisted root imaging analysis proved to be an informative and relatively highly automated phenotyping protocol. A QTL interval mapping was conducted using a segregating population at the seedling stage grown in controlled environment. Results enabled to narrow down the QTL interval and to identify new polymorphic markers for MAS in field experiments. A collection of homozygous recombinant NILs was developed by screening segregating populations with markers flanking qroot-yield-1.06. A first set of lines from this collection was phenotyped based on the adapted shovelomics protocol. QTL analysis based on these data highlighted an interval of 1.3 Mb as completely linked with the target QTL but, a larger safer interval of 4.1 Mb was selected for further investigations. QTL meta-analysis allows to synthetize information on root QTLs and two mQTLs were identified in the qroot-yield-1.06 interval. Trascriptomics analysis based on RNA-seq data of the two contrasting QTL-NILs, confirmed alternative haplotypes at chromosome bin 1.06. qroot-yield-1.06 has now been delimited to a 4.1-Mb interval, and thanks to the availability of additional untested homozygous recombinant NILs, the potentially achievable mapping resolution at qroot-yield-1.06 is c. 50 kb.

Three maize populations developed for their ability to withstand drought and salinity, and their reciprocal F1 crosses were tested under induced water stress and normal moisture conditions. Two commercial hybrids and one open-pollinated variety were also included in the study. The objective was to investigate yield and its components under induced drought. Significant differences in yield were observed in both irrigation treatments. DeKalb 689, one of the commercial hybrids, outyielded all the other entries under wet conditions, whereas under dry conditions the open-pollinated variety, Page Ranch, had the highest yield. Significant differences between populations and their hybrids were also observed. Significant correlations were noted in grain yield as observed in wet and dry conditions and the reduction in the number of ears per plant was positively correlated with the reduction in grain yield resulting from drought.

Mestrado Bolonha em Econometria Aplicada e Previsão
Nowadays, maize is the most important cereal in the world and its production has been increasing both worldwide and in Portugal, over the years. The constant technological development has led to the creation of new techniques such as precision agriculture, to better meet the global needs of this primordial cereal as well as optimize its production. This research was developed jointly with the firm Agro Analítica from the agriculture sector, whose area of expertise is Precision Agriculture and System Optimization. In this manner, the present work aims to estimate a function for the maize yield identifying the relevant determining factors, and their effect, on maize productivity on an exploitation of a firm in Azinhaga, Golegã, district of Santarém, Portugal for the year 2020. Using appropriate software, this dissertation applies the most recent spatial econometric methods to cross-sectional data, in order to properly include spatial dependence in the estimation. Thus, the appropriate models were estimated: Spatial Lag Model (SLM), Spatial Error Model (SEM) and SARAR(1,1) Model, whose use was recommended by the diagnosis to OLS (Ordinary Least Square) residuals. The elected model was the SARAR(1,1), capturing the spatial dependence and heteroscedasticity in the data, with an accuracy of approximately 90%. In this framework, it was concluded that maize yield, in the year and area under study, is positively influenced by factors such as the sowing density, applied sulfur trioxide (SO3) and a specific variety of seed. Regarding the fertilization, nitrogen and potassium, and irrigation of the crop, presented a non-linear (quadratic) relationship with the maize yield. Also influencing the yield, there are weather-related variables measured by stage of the maize life cycle, that prove to be significant at explaining the variable under study such as the relative humidity, the temperature, and the wind velocity.
Atualmente, o milho é o cereal mais importante do mundo tendo a sua produção vindo a aumentar tanto a nível mundial como em Portugal ao longo dos anos. O constante desenvolvimento tecnológico resultou na criação de novas técnicas, como a agricultura de precisão, para melhor satisfazer as necessidades globais deste cereal primordial bem como otimizar a sua produção. Esta investigação foi desenvolvida em conjunto com a empresa Agro Analítica do sector da agricultura, cuja área de especialização é Agricultura de Precisão e Otimização de Sistemas. Desta forma, o presente trabalho visa estimar uma função que explique a produtividade do milho identificando os fatores, e o seu efeito na produtividade do milho, numa exploração da empresa em Azinhaga, Golegã, distrito de Santarém, Portugal, para o ano 2020. Utilizando o software apropriado, esta dissertação aplica os mais recentes métodos e ferramentas econométricas espaciais para dados cross-section (dados transversais), de modo a incluir devidamente a dependência espacial na estimação. Assim, foram estimados os modelos apropriados: Modelo Spatial Lag (SLM), Modelo Spatial Error (SEM) e Modelo SARAR(1,1) (Kelejian & Prucha, 2010), cuja utilização foi recomendada pelo diagnóstico aos reísduos OLS (Ordinary Least Square). O modelo escolhido foi o SARAR(1,1), captando a dependência espacial e heterocedasticidade presente nos dados. Desta forma, concluiu-se que a produtividade do milho, no ano e na área em estudo, encontra-se positivamente influenciado por fatores como a densidade de sementeira, o trióxido de enxofre aplicado (SO3) e uma variedade específica de sementes. Quanto à fertilização, com azoto e potássio, e quanto à irrigação da cultura, estes fatores apresentaram uma relação não linear (quadrática) com a produtividade do milho. Também influenciando a produtividade, existem variáveis relacionadas com o clima, medidas pela fase do ciclo de vida do milho, que provaram ser significativas para explicar a variável em estudo, tal como a humidade relativa, a temperatura e a velocidade do vento.
info:eu-repo/semantics/publishedVersion

Master of Science
Department of Agricultural Economics
Timothy J. Dalton
In Kenya, agriculture governs the country’s fiscal economy, and this reliance on agriculture can cause both economic and hunger problems, a result of the country’s dependence upon rainfall for agricultural production. Kenyans must find ways to combat severe drought conditions; this can be accomplished through the adoption of inputs that decrease the probability of crop failure. The objective of this research is to determine whether variability exists in Kenyan maize yields, and whether or not specific inputs, specifically hybrid varieties, are either variance/skewness increasing or decreasing. The data used for this study was collected from a survey, designed by Egerton University’s Tegemeo Institute of Agricultural Policy and Development and Michigan State University, and administered in Kenya in the following years: 1997, 2000, 2004, and 2007. The survey identified factors of crop and field level production, such as inputs, crop mix, marketing data, and demographic information. This research makes use of only the 2007 data, comprising 1,397 households in total. The objectives of this thesis aim to go beyond the scope of typical production function regressions where yield is a function of a set of inputs, by examining further moments of yield, variance, and skewness to determine whether variability exists in Kenyan maize yields. Results indicate that variability does exist within Kenyan maize yields, often a result of differing input levels among households. In terms of overall impact of each variable on mean, variance, and skewness of maize yields, seed quantity, nitrogen use, and hybrid seed contribute the most to influencing these factors. In contrast, years of experience with hybrid maize, land tenure, terraced land and labor have the least influence on mean, variance and skewness within this research. Results also bring to light the popular debate against hybrid varieties versus open pollinated (OPV) or traditional varieties, and identify hybrid varieties as a source of variability in mean, variance and skewness of yields. Hybrid varieties should be paired with the knowledge of how to maximize yield in conjunction with other inputs, to give Kenya the opportunity to see substantial productivity gains throughout the country, especially in arid and semi-arid regions.

O milho (Zea mays) é considerado como uma das culturas mais importantes cultivadas mundialmente devido a sua composição química, valor nutritivo e o seu potencial produtivo, apresentando assim, considerável relevância nos aspectos socioeconômicos. Diversos fatores interferem no desempenho da cultura e, dentre eles, o clima está entre aqueles que oferecem os maiores desafios para planejamento e manejo da cultura. Diante da importância da cultura no contexto nacional e mundial, é importante considerar as projeções futuras da produção do grão diante das mudanças climáticas e, consequentemente, na segurança alimentar nos próximos anos. Assim, avaliou-se neste estudo o impacto da mudança do clima sobre o crescimento e desenvolvimento da cultura do milho, utilizando um modelo de crescimento de plantas, baseado em processos biofísicos. Para a calibração do modelo foram utilizados dados obtidos experimentalmente e a simulação de cenários de mudanças climáticas foi realizada de acordo com a abordagem do programa AgMIP. Trabalhou-se com o modelo CERES-MAIZE/DSSAT, e três modelos de circulação climática global (GCM\'s) regionalizados e dois cenários econômicos (ou de emissão) para o período 2040-2069 (representando 2050). Com base nos resultados obtidos, pode-se concluir que se as práticas de gestão se mantêm como presentes, o rendimento de milho deverá diminuir em meio do século, no entanto, a diminuição dos rendimentos reais pode não ser tão dramática quanto previsto nos casos em que apenas o fator climático é considerado. Para isso fatores econômicos e tecnológicos devem ser considerados para aumentar os rendimentos. O aumento da [CO2] terá um efeito positivo sobre o crescimento do cultivo, mas não parece ser suficiente para compensar os efeitos negativos do clima futuro, notadamente o aumento da temperatura do ar.
Maize (Zea mays) is considered one of the most important crops cultivated worldwide due to its chemical composition, nutritional value and its productive potential, thus presenting considerable relevance in socioeconomic aspects. Several factors interfere in the performance of the crop and, among them, the climate is among those that offer the greatest challenges for crop planning and management. Given the importance of culture in the national and global context, it is important to consider the future projections of grain production in the face of climate change and, consequently, food security in the coming years. Thus, the impact of climate change on maize crop growth and development was evaluated in this study using a plant growth model based on biophysical processes. For the calibration of the model, data obtained experimentally were used and the simulation of climate change scenarios was performed according to the AgMIP program approach. We worked with the CERES-MAIZE / DSSAT model, and three regional climate circulation models (GCM\'s) and two economic (or emission) scenarios for the period 2040-2069 (representing 2050). Based on the results obtained, it can be concluded that if management practices remain as present, corn yields should decrease in the middle of the century, however, the decrease in real incomes may not be as dramatic as predicted in cases where that only the climatic factor is considered. For this economic and technological factors must be considered to increase incomes. The increase in [CO2] will have a positive effect on crop growth, but it does not appear to be sufficient to compensate for the negative effects of future climate, notably the increase in air temperature.

Crop production must be increased substantially in the near future to maintain the present balance with food demand. As a large increase in growing area seems unthinkable, we must further increase crop yields significantly. Climate model projections suggest that higher temperatures will become commonplace in most regions where grain crops are produced, and deleterious effects of high temperature on crop yields are well documented. In this context, it is critical identifying genetic and management tools to mitigate the effect of high temperatures on yield. Nitrogen (N) fertilisation is one of the most widely applied management practices in grain crops worldwide. In many regions, crops are frequently well fertilised to maximise productivity. However, there have been limited efforts to elucidate to what degree the level of soil fertility may affect the magnitude of the high temperature effect on crop yield. Analysing the likely interaction may be relevant for designing more appropriate fertilisation strategies to not only increase productivity through better growth conditions but also to mitigate the likely yield penalties imposed by high temperatures. The general objective of this thesis was to assess the genotypic variability in yield components, and the susceptibility of yield determinants to thermal stress and nitrogen availability in maize. The issue was explored throughout 11 field experiments, carried out during 4 years, at two locations of contrasting altitude, under varying N fertilization regimes and a control with up to 12 different maize hybrids of contrasting maturity groups. In 4 of the field experiments different high temperature stresses were imposed, in combination with genotypes and N regimes, at the field by enclosing the designated area for the treatments with transparent polyethylene film (100 μm thickness) mounted in wood structures of 3-3.5 m height. In several of the experiments source-sink manipulations were also imposed to ascertain the origin of the yield penalties imposed by the different treatments. Differences in yield performance among hybrids were not related to the cycle duration, however if the comparison is restricted to the average of all short- and long-cycle hybrids, it can be confirmed that the shorter-cycle hybrids had lower production than the long-cycle hybrids. In parallel but independent set of experiments it was found that long cycle hybrids may be a true option for the high altitude farmers (if they are prepared to assume a higher than usual risk of loses in exceptionally cold autumns), as well as the short-cycle hybrids may be a reasonably productive alternative for farmers in the plain of Lleida (and other similar environments). Overall the range of conditions, yield was more strongly affected by capture, than by partitioning or efficiency of use of resources and was positively related to both of its components similarly (even though grain number was more plastic than grain weight) as well as to grain protein concentration. The negative relationship between yield and Nitrogen Utilisation efficiency (NUtE) found in the context of the wide range of conditions did not preclude the awareness that future hybrids shall be more NU Efficient and that ways to select for improved Nitrogen Use Efficiency (NUE) must be developed for future agricultural systems in which N is expected to be less freely available while yields must keep increased. Then, recently proposed surrogate for phenotyping to improved NUE (the critical specific leaf N, SLNc) was tested for genetic variation. It was proven that large genetic variation exists for SLNc, partly related to genotypic differences in N uptake N uptake . This would imply that SLNc would hardly be a good surrogate to phenotype large populations for improved NUE. It was demonstrated for the first time in maize that the sensitivity of yield to heat stress was increased by N fertilisation. This conclusion is based on field experiments with treatments of a magnitude well within expected variation in realistic conditions. The effect was through affecting the capacity of the plants to set grains and to a lesser extent to allow grain weight to be maximised; and it was independent of any (potentially additional) effects on either uncoupling anthesis and silking or on pollen amount and viability. Heat stress affected grain size by directly affecting the capacity of the grains to grow. This conclusion was reached both due to interpretations on the effects of heat on source-sink relationships of plants as well as from results of manipulations of the source-sink relationships during grain filling. Heat stress reduced grain size even when it increased source-sink ratio (by inducing late abortion of few grains while not affecting much post silking growth), and this direct effect was not worsened by defoliation nor reversed by degraining, and the penalty did not exhibit a clear hierarchical response: it was similar for grains of different potential size.
En un futuro próximo la producción de los cultivos deberá ser sustancialmente incrementada para poder abastecer la demanda de alimentos. Como futuros aumentos en el área de producción no es posible, la única forma, es aumentar de manera significativa los rendimientos de los cultivos. Las projeccions con modelos climáticos sugieren que la frecuencia de altas temperaturas serán cada vez mayores en la nayoría de las regiones donde se producen cultivos extensivos, y se encuentra muy bien documentado los efectos deletéreos de las altas temperaturas sobre la productividad de los cultivos. En este contexto, será fundamental la identificación de genotipos y esrategias de manejo para mitigar los efectos de altas temperaturas sobre productividad de los cultivos. A nivel mundial, la fertilización nitrogenada (N) es una de las prácticas de manejo ampliamente utilizada en los sistemas agrícolas. En muchas regiones, los cultivos son frecuentemente fertilizados para maximizar la productividad. Sin embargo, han habido pocos esfuerzos para elucidar en qué medida el nivel de fertilidad del suelo puede afectar la magnitud de las altas temperaturas sobre la productividad de los cultivos. El análisis de una posible interacción entre las altas temperaturas y el nivel de nitrógeno en el suelo puede ser relevante para el diseño de estrategias apropiadas de fertilización no sólo para aumentar la producción a través de mejorar las condiciones de crecimiento sino también para mitigar los posibles efectos negativos impuestos por las altas temperaturas. El objetivo general de esta tesis fue evaluar la variabilidad genotípica en los componentes del rendimiento, y la susceptibilidad de los determinantes del rendimiento al estrés térmico combinado con diferentes disponibilidades de N en el cultivo de maíz. El tema fue explorado a lo largo de 11 experimentos en campo llevados a cabo durante 4 años consecutivos y en dos localidades contrastante en altitud, para ello se utilizaron 12 híbridos de maíz de grupos contrastante en madurez bajo diferentes condiciones de fertilización nitrogenada, además de un control sin fertilizar. En 4 de los experimentos de campo, en una combinación de genotipos y regímenes de nitrógeno se impusieron diferentes estreses de altas temperaturas, para ello se cubrió el área designada para los tratamientos con plástico transparente de polietileno (100 μm de espesor) montada en estructuras de madera de 3-3.5 m de altura. Además, en varios experimentos se impusieron diferentes tratamientos de manipulación de fuente-sumidero para determinar el origen de la limitación del rendimiento impuesto por efectos de las elevadas temperaturas. Las diferencias en rendimiento entre los híbridos no se relacionaron con la duración del ciclo. Sin embargo, si la comparación se limita a la media de los rendimientos observados de todos los híbridos de ciclo corto y largo, se confirma que los híbridos de ciclo corto tuvieron menor producción en comparación con los de ciclo largo. Paralelamente, pero en experimentos independientemente se determinó que los híbridos de ciclo largo pueden ser una verdadera opción para agricultores en condiciones de elevadas alturas tal como en los valles del pirineo (en caso de poder asumir un mayor riesgo que lo habitual de perder la cosecha en otoños con fríos excepcionales), adicionalmente los híbridos de ciclo corto pueden ser una alternativa razonable de producción para agricultores en la plana de Lleida (y otros ambientes similares). En el conjunto de condiciones evaluadas, el rendimiento estuvo mayormente afectado por la captura mas que por la partición o el uso eficiente de los recursos, en los cuales la relación fue positiva y de igual magnitud en ambos componentes del rendimiento (a pesar de que el número de granos fue más plástico que el peso de los granos), al igual que ocurrió con la concentración de proteína en los granos. La relación negativa entre el rendimiento y NUE encontrado en el contexto de la amplia gama de condiciones no se opone a la idea de que los híbridos en el futuro deberán ser más eficientes en NU y que formas de seleccionar para mejorar NUE deberán ser desarrolladas para los sistemas agrícolas futuros en los que se espera que el N será de menor disposición mientras que los rendimientos deben seguir aumentado. Recientemente fue propuesta una alternativa de fenotipeo para mejorar la eficiencia del uso del nitrógeno (el nitrógeno específico crítico en las hojas, SLNc), y esta variable fue utilitzada para evaluar la variabilidad genética. Se determinó que existe una amplia variación genética para SLNc, y parcialmente estuvo relacionado con las diferencias genotípicas en la absorción del nitrógeno. Esto implica que SLNc difícilmente sería una buena alternativa para fenotipeo de grandes poblaciones y mejorar el uso eficiente del nitrógeno. Se demostró por primera vez en esta tesis, que en el cultivo de maíz, la sensibilidad del rendimiento al estrés térmico fue aumentada con la fertilización nitrogenada. Esta conclusión se basa en experimentos de campo con tratamientos con una magnitud de variación similares a las que se esperada en condiciones reales. El efecto fue a través de afectar en las plantas la capacidad para el cuajado de los granos y en menor medida el crecimiento; y esto fue independiente a cualquier (adicional potencial) efecto por el desfase entre la floración masculina yfemenina, o por la disponibilidad y viabilidad del polen. El efecto del estrés térmico en el tamaño potencial de los granos fue directamente a través de afectar su capacidad para crecer. Estas conclusiones se alcanzaron debido tanto a las interpretaciones de los efectos de las altas temperaturas en las relaciones fuente- sumidero propias de las plantas, así como también de resultados de las manipulaciones en la relación fuente-sumidero durante el llenado de grano. El estrés térmico resultó en una reducción del tamaño de los granos incluso cuando se aumentó la relación fuente sumidero (mediante la inducción de aborto tardío de pocos granos sin afectar mucho el crecimiento post-floración), y ese efecto directo no fue empeorado por la defoliación ni revertido por el desgrane, y la penalización no exhibió una respuesta jerarquica clara: fue similar para todos los granos independientemente del tamaño potencial.
La producció de cultius ha d’incrementar-se substancialment a curt termini per mantenir l’equilibri amb la demanda alimentaria mundial. Atès que un gran increment de superfície cultivada sembla impensable, l’increment de producció ha de venir per un increment en el rendiment. Els models climàtics suggereixen que temperatures més elevades que les actuals seran habituals en moltes regions del mon on es conreen cultius per a gra, i en aquests, estan ben documentats efectes deleteris degut a les altes temperatures. En aquest escenari, és crític la identificació d’aspectes genetics i de la gestió d’eines per mitigar el efecte de les elevades temperatures sobre el rendiment. La fertilització nitrogenada (N) és una de les pràctiques de maneig més esteses en els cereals de gra arreu del món i en moltes regions els conreus per a gra es fertilitzen bé per a maximitzar la producció. Malgrat això, els esforços per explicar fins a que punt la fertilitat del sòl pot afectar l’efecte de l’elevada temperatura sobre el cultiu son limitats. Analitzar la possible interacció entre la fertilització i les temperatures pot ser rellevant per dissenyar estratègies de fertilització més apropiades no solament per a incrementar la productivitat sino per a mitigar les possibles penalitzacions de les altes temperatures sobre el rendiment. L’objectiu general d’aquesta tesi és l’avaluació de la variabilitat genotípica en els components del rendiment i la susceptibilitat d’aquests components del rendiment al estrès tèrmic de forma combinada amb la disponibilitat de nitrogen en blat de moro. L’estudi es va portar a terme mitjançant 11 experiments de camp, portats a terme durant 4 anys, en dos localitats contrastants en altitud, sota diferents règims de fertilització nitrogenada en 12 diferents híbrids de blat de moro de diferents grups de maduració. En 4 dels experiments de camp es van imposar diferents estresses de temperatures elevades en combinació amb diferents hibrids de panis i diferents règims de nitrogen, mitjançant l’envoltament d’una zona determinada amb estructures de fusta de 3-3,5m d’altura cobertes amb polietilè transparent (100 micres). En varis dels experiments es van realitzar també manipulacions font-embornall de manera factorial per establir l’origen de las penalitzacions en rendiment dels diferents tractaments. Les diferències en la resposta del rendiment dels diferents híbrids no van estar relacionades amb la duració del cicle del híbrid, no obstant això si la comparació es restringeix a la mitjana de tots els híbrids de cicle- curt i els de cicle-llarg, els híbrids de cicle-curt van tenir produccions més baixes que els de cicle-llarg. En paral·lel, però en un grup d’experiments independent és va observar que els híbrids de cicle (relativament)-llarg podrien ser una bona opció pels agricultors que cultiven en altituds elevades (si estan preparats per assumir un risc més elevat del habitual de pèrdues degudes a tardors excepcionalment fredes). Així mateix, els híbrids de cicle-curt podrien ser una alternativa de producció raonable per pagesos en la plana de Lleida (i altres ambients similars). En general pel conjunt de les condicions estudiades, el rendiment de gra va resultar estar més afectat per la captura de los recursos (aigua, N, etc.) que pel seu repartiment o per l’ús eficient dels mateixos, i va ser positivament relacionat amb ambdós components de rendiment amb igual magnitud (encara que el numero de grans va ser més plàstic que el pes del grans) així com amb la concentració de proteïna al gra. La relació negativa entre el rendiment i l’eficiència del l’ús del nitrogen (nitrogen use efficiency, NUE) trobada en aquest context d’ample varietat de condicions, no pot descartar el fet de que híbrids futurs haurien de ser més eficients en l’ús del nitrogen. Per tant cal desenvolupar noves eines de selecció per millorar NUE pels futurs híbrids i sistemes agrícoles en els que es preveu que el N estarà menys disponible, al mateix temps que s’ha de continuar incrementant el rendiment. Un estudi recent va proposar l’estudi del contingut específic de nitrogen en fulla (critical Specific Leaf Nitrogen, SLNc). Aquest estudi va demostrar que existeix una gran variabilitat genètica per SLNc, en part relacionada amb diferencies genètiques en l’absorció de N. Aquest implicaria que el SNLc difícilment podria ser una bona alternativa per l’estudi del fenotip de grans poblacions per millorar l’eficiència del l’ús del nitrogen. En aquesta tesi s’ha demostrat per primera vegada en blat de moro que la sensibilitat del rendiment al estrès tèrmic és va incrementar amb la fertilització nitrogenada. Aquesta conclusió està basada en experiments de camp amb condicions realistes, reflectint de manera molt similar les variacions ambientals esperades (tèrmiques, aigua, N, etc.). L’efecte es va observar en la capacitat de les plantes per establir grans i en menor grau en permetre maximitzar el pes del gra i va ser independent de qualsevol efecte potencial del acoblament en la fecundació (sortida de sedes – alliberació del polen) o en la quantitat i viabilitat del pol·len. L’estrés tèrmic va afectar la grandària del gra afectant directament la seva capacitat de creixement. A aquesta conclusió s´hi va arribar a partir de les interpretacions del efecte de temperatures elevades sobre les relacions font-embornall de les plantes i dels resultats de les manipulacions de las relacions font-embornall durant l’etapa d’omplenament del gra. L’estrès tèrmic va reduir la grandària del gra inclús quan es va incrementar la relació font-embornall (induint la aborció tardana dels pocs grans al temps que no s’afecta el creixement després de la sortida de sedes) i aquest efecte directe no va ser empitjorat ni per la defoliació ni per el desgranat i la penalització no va mostrar cap resposta jeràrquica clara: va ser similar en grans amb diferent grandària potencial.

Nitrogen (N) fertilization and drought stress have large influence on maize grain yield, thus studies about genotypes and management technologies are very important to increase maize production. This study is presented in three chapters; the first two were undertaken in the United States of America and the third one in Brazil. The following objectives are addressed in this order: (1) The primary objective was to understand which traits, if any, differ between similar-maturity tolerant and non-drought tolerant hybrids that govern nutrient uptake and concentrations under different management treatments (varied plant densities (PD) and N rates) and their influence on grain yield (GY). (2) The primary objective was to investigate the physiological and yield responses of comparable-maturity drought and non-drought tolerant hybrids (P1151 vs. P1162, and P1498 vs. 33D49) to varied plant density and N rates. (3) The main objective was to investigate the responses of maize to sidedress N applications, using isotopically labeled urea fertilizer (15N), at different development stages. The secondary objective was to verify the correlations between the chlorophylls and carotenoids with SPAD index (evaluated at V14 and V16) and all these parameters with total biomass (BM), harvest index (HI), GY and grain N content. The major results for objectives 1 and 2 were as follows: All hybrids had similar GY responses to PD (near 79,000 versus near 100,000 plants ha-1) and N rate (from 0 to 269 kg N ha-1) treatment factors. Hybrid 1 (AQUAmax(TM) P1151) demonstrated similar leaf photosynthetic (A) and transpiration (E ) rates than its non-drought tolerant counterpart of similar maturity since Hybrid 2 (P1162) had a higher leaf area Index (LAI) (at the R2 and R3 stages) and a similar GY as Hybrid 1. Hybrid AQUAmax(TM) P1498 maintained higher leaf A and E rates than P33D49 during the grain-fill period, thus perhaps demonstrating improved persistence in root water uptake late in the season. There was no single trait differentiation in photosynthesis or transpiration between drought and non-drought tolerant hybrids. Highest BM and GY at maturity generally followed shorter anthesis-silking intervals and more stover macronutrient (P and S) accumulation, in the drought season, so these characteristics appeared to be important drought-tolerant mechanisms regardless of hybrid designations. The major findings from the objective 3 investigations: Maize crop responded similarly for GY to timing of sidedress N application. Grain N content from 15N fertilizer and N uptake and efficiency were greater for early N applications. SPAD values correlated positively with most pigment variables at V16 in both seasons, thus proving that SPAD was an efficient instrument of indirect evaluation of chlorophylls and carotenoids in maize leaves at early stages. Chlorophyll b at V16, sample stage, was positively correlated (P<0.05) with grain N content, GY, and BM, and total chlorophyll at V16 was positively correlated with GY and grain N content. However the chlorophylls a and total, evaluated at V14, were negatively correlated with GY. So, measurement chlorophyll and carotenoid pigment contents should be done after V14 stage when studies aim to evaluate crop nutritional conditions and prescribe future grain production practices.
Adubação nitrogenada (N) e o estresse hídrico tem grande influência no rendimento de grãos de milho, assim, estudos sobre genótipos e o manejo dessa cultura são muito importantes para o aumento da produtividade. Este estudo é apresentado em três capítulos. Os dois primeiros foram desenvolvidos nos Estados Unidos e o terceiro no Brasil. Os objetivos são apresentados na seguinte ordem: (1) o objetivo principal foi entender quais características, se existirem, diferem entre híbridos tolerantes e não-tolerantes à seca, com semelhança em maturidade, que regem a absorção de nutrientes e concentrações destes sob diferentes tratamentos de cultivo e sua influência na produção de grãos. (2) O objetivo principal foi investigar as respostas fisiológicas (fotossíntese (A) e transpiração (E)) e a produção de milho em genótipos, com semelhante maturidade, tolerantes e não tolerantes ao déficit hídrico (P1151 vs. P1162 e P1498 vs. 33D49) em relação a variação de densidade de plantas e doses de N. (3) O principal objetivo foi investigar as respostas de milho à aplicação de nitrogênio em cobertura, ureia fertilizante (15N), em diferentes estádios fenológicos. O objetivo secundário foi: verificar a correlação entre as clorofilas e carotenoides com SPAD (avaliado em V14 e V16) e destas com a biomassa total (BM), índice de colheita (IC), produção de grãos (PG) e do conteúdo de N nos grãos. Como resultados: (1 e 2) Todos os híbridos responderam de forma semelhante para para PG em relação aos tratamentos. O Híbrido P1151 demonstrou semelhantes A e E e menor area foliar do que seu semelhante em maturidade (P1162). Híbrido P1498 pareceu ser capaz de manter a taxa de transpiração foliar e de fotossíntese mais elevadas do que 33D49, durante o período de enchimento de grãos. Este híbrido apresentou uma melhor persistência na captação de água pela raiz no final da estação de cultivo. Geralmente maiores BM e PG na maturidade foram relacionadas a menores intervalos de diferenciação floral e a maior acumulação, na estação seca, de macronutrientes (P e S) no colmo, sendo as ultimas características consideradas como mecanismos de tolerância à seca. (3) A cultura do milho respondeu de forma semelhante em relação a PG à aplicação de N. O teor de nitrogênio nos grãos derivado do 15N fertilizante e a eficiência de uso do fertilizante nitrogenado foram maiores em relação a aplicação de N nos primeiros estádios. Houve correlação positiva e siginificativa para SPAD com a maioria dos pigmentos no estádio de avaliação V16. Provando ser um instrumento eficaz de avaliação indireta de clorofilas e carotenóides em estágios iniciais. A clorofila b, avaliada em V16, apresentou correlação positiva significativa (p<0,05) com teor de N nos grãos, PG, e BM, a clorofila total em V16 também apresentou uma correlação positiva com o teor de N nos grãos, no entanto, as clorofilas a e total, avaliadas em V14, apresentaram correlação negativa com PG. Assim, a medição do teor de pigmentos com o objetivo de estudar as condições nutricionais e previr a produção de grãos deve ser realizada após o estágio V14.

Orientador: Carlos Alexandre Costa Crusciol
Banca: Patricia Preira Dias
Banca: Claudio Hideo Martins da Costa
Resumo: A crescente demanda por fertilizantes concomitante ao aumento dos preços desse insumo e a escassez de suas fontes levam a incessante busca por fontes alternativas de nutrientes para as plantas. Os afloramentos rochosos no Brasil coincidem com as localidades de áreas produtivas, tornando o acesso fácil dos produtores rurais à essas fontes, uma vez que o maior custo do pó de rocha está relacionado ao frete. Portanto, uma das alternativas estudadas é o uso de pó de dunito, rico em magnésio em culturas anuais, como soja e milho. Estas são uma das principais culturas do Brasil em área de produção. O objetivo desse estudo foi avaliar os efeitos de doses de pó de dunito no teor foliar de Magnésio (Mg) e Silício (Si), teores foliares de açúcares redutores, sacarose e amido, e atributos químicos de solo em dois tipos de solo. Os tratamentos consistiram em cinco doses de pó de dunito (0, 42, 208, 542 and 1542 mg kg-1) no solo argiloso e (0, 150, 238, 411 and 933 mg kg-1) no solo arenoso, respectivamente. Em ambos os solos, os teores de Mg e Si foliar, os açúcares redutores e glicose nas folhas, assim como pH, Mg, e Si do solo e os componentes de produção aumentaram com o aumento das doses de dunito. A melhor nutrição de Mg fornece menor teor de amido foliar e consequentemente melhor partição de metabolitos na planta, levando ao melhor desenvolvimento, enchimento e produção de grãos de soja.
Abstract: The growing demand for fertilizers, coupled with the increase in fertilizer prices and the scarcity of fertilizer sources, lead to the incessant search for alternative sources of nutrients for the plants. The rocky outcrops in Brazil coincide with the localities of agriculture productive areas, making access easy for rural producers to these sources, since the higher cost of rock dust is related to the transport. Therefore, one of the alternatives studied is the use of dunite powder, rich in magnesium in annual crops such as soybean and corn. These are one of the main crops of Brazil in production area. The aim of this study was to evaluate the effect of dunite rates on Magnesium (Mg), Silicon (Si), foliar contents of reducing sugars, sucrose, and starch, soil chemical attributes and soybean yield in two soil types. The treatments consisted in the five rates of Dunite (0, 42, 208, 542 and 1542 mg kg-1) in a clayey soil, and five rates of Dunite (0, 150, 238, 411 and 933 mg kg-1) in a sandy soil. In both soils, the Mg and Si leaves concentration, foliar reducing sugars, and glucose, as well as soil pH, Mg, and Si, and the yield components increased with input rates. The best Mg nutrition provides lower foliar starch levels, consequently, the best partition of metabolites to plant leads to better development, filling and yield of soybeans.
Mestre

The effect of management practices used by smallholder farmers to improve soil quality and increase maize yield was examined in an 80 ha. micro-watershed of central Malawi. Because of the complexity inherent in smallholder farming systems, this research proposed the combination of participatory methods with analytical techniques developed in field ecology, such as multivariate and spatial analysis. During a Participatory Rural Appraisal (PRA), farmers identified factors potentially influencing soil quality and maize yield. One hundred and seventy-six (176) plots were located in twenty-nine (29) fields and characterized for management practices and biophysical characteristics. Soil samples were collected at each plot and analysed for a suite of properties. The maize yield was measured for both 1996--97 and 1997--98 seasons. A formal survey was used to gather information on household characteristics. Results showed that management practices that were promoted by a previous extension project, such as alley cropping and the planting of grass on contour ridges, were strongly correlated and found mainly in fields located closer to house compounds. Farmers with a higher proportion of their land under wetland gardens tended to use less agroforestry. Food security was associated with households that were able to purchase inorganic fertilizers, had larger landholding size, and owned livestock and woodlots. The effect of management practices on maize yield and soil quality was partially confounded with characteristics of the plot, such as slope, degradation level, number of years under cultivation or pest damage. Higher maize yield was observed in plots that were better managed, as expressed by the combination of different management practices, lower pest incidence, fewer erosion signs and higher soil fertility. Some positive effects of alley cropping on soil quality were observed in plots that were cultivated for a longer period and located on flatter land. This study demo

In general, yield reduction in most dryland maize growing areas of South Africa occur because seasonal rainfall distribution is erratic with annual variation that cannot be predicted accurately. Cultivar selection, planting date and plant density are other factors that consistently affect maize yield. Long growing season maize cultivars are higher yielding, particularly under conditions of good moisture and nutrient supply. However, as both moisture and nutrient availability becomes more limiting, yield tends to decline. Short growing season maize cultivars could yield more than long season counterparts because they can maximize the growing season and potentially reach the critical flowering stage before traditional midsummer droughts occur. The short growing season maize cultivars, which have only recently been developed, have traits, which can address the problem of reduced yield, which is ascribed to midsummer drought. There has been no previous effort to evaluate the effects of planting dates and plant densities on yield and yield components of these short and ultra-short growth period maize cultivars. This prompted research in the 2004/05 growing season. One field experiment was conducted at each of two selected areas (Bethlehem&Potchefstroom) in the “Maize Triangle” of South Africa. The aim was to evaluate the response of short and ultra-short growth period maize cultivars to planting dates and plant densities at two localities with distinct environmental conditions. The effects of planting date, plant density and cultivar on yield and yield components were investigated. Both yield and yield components were affected by planting date, plant density and cultivar at both localities. At both localities early and optimum planting dates as well as low and optimum plant densities promoted increases in yield components, which contributed to increased grain yield. As for the cultivars, PAN6017 proved to be the most consistent since it out-performed other cultivars in terms of both vegetative growth, yield components and grain yield at both localities. At both localities, plant height, leaf area index and dry matter yield were affected by both planting date and plant density, with optimum planting date and optimum plant density contributing to highest yield components and yield. PAN 6017 was superior to the other cultivars at all planting dates and plant densities at both localities. In order to make findings from a study such as this applicable to the “Maize Triangle”, more research on short and ultra-short growth period maize cultivars should be conducted over a wider range of locations and seasons.
Dissertation (M Inst Agrar (Agronomy))--University of Pretoria, 2007.
Plant Production and Soil Science
M Inst Agrar
unrestricted

Review of the literature suggested possible deficiencies of micronutrients in soils of North Western Zambia. Soil analysis, pot and field experiments were employed to investigate possible deficiencies. The pot experiments investigated how raising soil pH through liming influenced extractable micronutrients and their uptake by plants. Plant Mo and Ca were positively correlated with soil pH, while Mn and Zn were inversely correlated, aggravating the zinc inadequacy on all soils and that for Mn on arenosols. Effects of liming on plant uptakes of micronutrients generally followed the same trends as those on soil extraction. Incubating the soil under grass house conditions was found to influence amounts of extractable micronutrients, increasing most times above their levels before the soil was incubated. Field experiments generally showed that applying micronutrients were beneficial to crop yield only at some sites. Grain yield variables responded variously and were most significantly correlated with overall grain yield. Soil analysis usefully predicted deficiencies of Zn for both maize and soybean. However, predictions for B and Mo were ideal for soybean than maize. Cu also seemed to have been wrongly predicted for soybean. However, plant nutrient concentration was better at predicting nutrient status in relation to grain yield, but the lower limits of the suggested optimal concentration ranges may need to be worked out again. Soybean was found to have more micronutrient latent deficiencies at majority of the sites than maize. One of the characteristics of applied micronutrients was their beneficial residual effects of crop yield. The residual benefit was also noticed on maize when the fertilisers were directly applied to soybeans a season before, suggesting a possibility of crop rotation, thus spreading the costs. Results would suggest changing the current fertiliser recommendations in the region.

Thesis (M.Sc. (Soil Science)) --University of Limpopo, 2013
Large amount of pre-plant nitrogen (N) fertilizer results in low nutrient-use-efficiency due to poor synchrony between soil N supply and maize demand, especially during N sensitive growth stages. Optimum maize production is dependent on adequate N availability to the crop during the critical vegetative and reproductive growth stages. High N fertilizer prices and maize yield decline are the main challenges faced by the Limpopo Province farmers. The objectives of this study were to compare growth and yield of maize under conventional and site-specific N management in a dryland farming system. The study was conducted in Leeukraal, Towoomba, Ga-Marishane and Radium in the Limpopo Province, South Africa. Experimental plots were laid out in a randomized complete block design, with four replications. Phosphorus was applied through band placement using a planter in all plots at a rate of 42 kg P/ha. Hybrid maize SNK 2147 was planted on a 20 by 20 m plot with Inter-row and Intra-row spacing of 0.9 and 0.35 m respectively. Treatments consisted of 3 N management strategies as follows, (i) No N application (N0), (ii) Site-specific N at a rate ranging between 18 and 33 kg N/ha (N1) and (iii) Conventional N application at 58 kg N/ha (N2). Treatment N2 was applied at a uniform rate during maize planting. Sufficiency index as an indication for N deficiency was determined using CCM-200 for treatment N1. The sufficiency index was determined during leaf stage V6, V10 and V14, and thereafter N was applied only when needed. Data were subjected to analysis of variance through Statistical Analysis System package. Mean separation tests were computed using Duncan’s Multiple Range Test. Maize grain yield at Leeukraal of 5.2 t/ha for N1 was higher than 3.2 and 4.0 t/ha of N0 and N2, respectively. There was no difference amongst the three N management approaches on the grain yield at Towoomba. The grain yield at Ga-Marishane for N1 of 2.2 t/ha was significantly higher than 1.7 t/ha of the N0. Conventional management approach, which is a traditional approach used by farmers in the Limpopo Province, had 2.6 t/ha grain yield that was significantly higher than the N0 and N1. The maize growth and yield under N2 and N1 was compared, N1 required between 43 and 69% lesser N fertilizer as compared to N2. Therefore site-specific nutrient management approach sustains and improves growth and yield of maize using minimal inputs of N compared to conventional approach. This therefore saves input costs and avoids unnecessary environmental consequences. Key words: maize yield, nitrogen management, site-specific approach
Vlaamse Interuniveritatire Raad and Limpopo Department of Agriculture

To achieve food security and meet environmental requirements, the average rates of major crop yields in crops such as maize are expected to increase instead of expansion of cultivated areas. Maize crop has as main factors responsible for the low yields in Brazil the water and nitrogen (N) deficits. The concept of yield gaps is the difference between the maximum yield that can be achieved in a given place, limited by water (Yw) or not (Yp), and the average yields, observed under practical conditions (Ya). This concept is of great importance for characterizing the range of maximum yields and definemanagement strategies to its mitigation. Yield potential (Yp) is determined by conditions of temperature, solar radiation, photoperiod and genetic potential; to Water-limited yield (Yw) is added the water limitation imposed by crops on rainfed condition. In this study we aimed to characterize the variability of yield gaps related to environmental and management conditions; and to evaluate the economic and energy returns related to management of these yield gaps through the mechanical application of nitrogen fertilizer in six regions located in the South Central portion of the country in two periods of maize cultivation (1st and 2nd maize growing seasons). Yield gaps related to water restriction (CYg = Yp - Yw) and imposed by management conditions (MYg = Yw - Ya) were determined through aid of integrated models DSSAT system (Decision Suport System for Agrotechnology Transfer). The maize model (CSM CERES-MAIZE) was calibrated with cultivars trial data obtained for the last few years in all evaluated regions. In the 1st growing season, Yp was higher and Yw was higher and more variable than on 2nd growing season due to climate variability. The yield gaps relative to management were more limiting than the gaps relative to water deficit in almost all the evaluated regions. In both crops\' growing seasons, higher and lower MYg were found in two regions of Southern and Midwestern portion of the country, respectively. Although both regions presented high average yields (Ya), different environmental conditions determined the largest absolute differences between their rates of Yp, Yw and MYg. When assessing the profitability (R$ k g-1, MJ kg-1, R $ ha-1; MJ ha-1) of N application as MYg reduction strategy, the behavior of the variation in yields with increasing rate of N was observed. In general, the diminishing returns showed higher use efficiency (per harvested yield and per unit area) at lower N rates (20-80 kg ha-1). Economic and energy profits (regardless of their rate of change related to the increased application of cost) were found at higher N rates (90-400 kg ha-1), and this limit is directly influenced by local climate conditions. Local management of MYg can be more or less viable depending on the combination of environmental conditions and usual management conditions. In general, the cost of N application is higher in 2nd growing season due to most limiting climatic conditions, but regions with efficient management of yield gapswere alsofound in 2nd growing season
Para alcançar a segurança alimentar e atender necessidades ambientais, os índices médios de produtividade de importantes culturas na alimentação como a do milho devem aumentar em detrimento da expansão de áreas cultivadas. A cultura do milho possui como principais fatores responsáveis pelos baixos índices de produtividade no Brasil os deficits hídrico e de nitrogênio (N). O conceito de quebra de produtividade (yield gaps) é a diferença entre a máxima produtividade que pode ser atingida em dado local, seja ela limitada pela água (Yw) ou não (Yp), e a produtividade média observada em condições práticas (Ya). Esse conceito é de grande importância para caracterização de limites de alcance de máximas produtividades e definição de estratégias de manejo para mitigação dos mesmos. A produtividade potencial (Yp) é aquela determinada pelas condições de temperatura, radiação solar, fotoperíodo e potencial genético; à produtividade limitada pela água (Yw) adiciona-se a limitação hídrica imposta por cultivos em sequeiro. Nesse estudo buscou-se caracterizara variabilidade das quebras de produtividade referentes às condições ambientais e de manejo; bem como avaliar o retorno econômico e energético do manejo dessas quebras por meio da aplicação mecanizada de fertilizante nitrogenado em seis municípios localizados na região Centro-Sul do país nas duas épocas de cultivo da cultura do milho (safra e safrinha). Quebras de produtividade referentes à restrição hídrica (CYg = Yp - Yw) e impostos pelas condições de manejo (MYg =Yw - Ya) foram determinadas com auxílio da utilização do sistema de modelos integrados DSSAT (Decision Suport System for Agrotechnology Transfer).O modelo da cultura do milho (CSM CERES-MAIZE) foi calibrado com dados de ensaio de cultivares, obtidos para os últimos anos em todas as regiões avaliadas. Na 1ª safra, os indices de Yp foram mais altos e os indices de Yw foram mais altos e variáveis devido à variabilidade climática.A quebra de produtividade relativa ao manejo foi mais limitante do que a quebra relativa ao deficit hídrico em quase todos os municípios avaliados. Em ambas as safras de cultivo, maiores e menores MYg foram encontrados em dois municípios das regiões Sul e Centro-Oeste do país, respectivamente. Apesar de ambas as regiões apresentarem altas produtividades medias (Ya), diferentes condições ambientais determinaram as maiores diferenças absolutas entre seus indices de Yp, Yw e MYg. Ao avaliar a rentabilidade (R$ kg-1; MJ kg-1; R$ ha-1; MJ ha-1) da aplicação de N como estratégia de redução de MYg, observou-se o comportamento da variação dos rendimentos de produtividade com o aumento das doses de N. Em termos gerais, os rendimentos decrescentes apresentaram maior eficiência de uso do insumo (por massa colhida e por unidade de área) nas menores doses de N (20-80 kg ha-1). Lucros econômicos e energéticos (sem considerar sua taxa de variação com relação ao aumento do custo de aplicação) foram encontrados até doses mais altas de N (90-400 kg ha-1), sendo que esse limite é diretamente influenciado pelas condições climáticas locais. O manejo local dos MYg pode ser mais ou menos viável em função da combinação das condições ambientais e de manejo usual locais. Em termos gerais, o custo de aplicação de N é maior na 2ª safra devido às condições climáticas mais limitantes, porém municípios com manejo eficiente da quebra de produtividade foram encontrados mesmo nas condições de cultivo do milho safrinha.

The research objectives were to examine the effect of soil nutrient status on the growth rate, reproductive development, yield components and yield of maize in a long-term trial. On the Experimental Farm of the University of Pretoria, treatments selected for this investigation were O (control), PK (nitrogen deficient), NK (phosphorus deficient), NP (potassium deficient), NPK (balanced nutrient), and WNPKM (mixture of balanced nutrient and manure). Growth analyses were performed, embryonic tassel and ear development recorded, developmental stages and rate of tasseling and silking were monitored while yield components were determined at maturity. The balanced nutrient treatment (WNPKM) plants showed the highest growth rate and produced the highest biomass while the P and K deficient treatments resulted in low growth rates and low biomass. The PK and NPK treatments were intermediate in terms of growth rate and biomass production. The WNPKM, NPK and PK treatments exhibited a high net assimilation rate (NAR) and crop growth rate (CGR), illustrating that an adequate supply of N, P and K is required for high growth rate and biomass production. Plants in the WNPKM plots exhibited early tassel initiation and ear differentiation and larger reproductive organs. Reproductive development in the PK treatment was ahead of those of the NP and NPK treatments. Nutrient stress delayed initiation and differentiation resulting in smaller reproductive organs. A linear relationship was found between leaf area indices (LAI) and the sizes of the reproductive structures. The higher the LAI the larger the size of the reproductive structures. Emergence of inflorescences was timely in plants exposed to the balanced nutrient but delayed in nutrient deficient treatments. Grain yield and the yield components were positively affected by the balanced nutrient treatment while the nutrient stress treatments reduced the yield. Copyright 2008, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Bello, ZA 2008, Effect of soil nutrient status on growth, reproductive development and yield components of maize in a long term field trial, MSc(Agric) dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-02122009-105701 / > E1251/gm
Dissertation (MSc(Agric))--University of Pretoria, 2008.
Plant Production and Soil Science
unrestricted

The effects of spatial arrangement and density on agronomic efficiency, yield and yield components, dry matter partitioning and growth of an annual cotton/cowpea/maize intercrop were examined in 1990 and 1991 in Tucson, Arizona. The 1990 experiment consisted of four spatial arrangements crossed with four densities of cowpea and maize in a complete factorial design. The 1991 experiment consisted of two densities of cowpea and maize selected from the 1990 experiment in the best spatial arrangement crossed with five densities of cotton in a complete factorial design. A land use efficiency of 12% (or a land equivalent ratio of 1.12) was obtained in the spatial arrangement of single rows of cowpea and maize between singles rows of cotton, whereas a land use efficiency of 11% was obtained for cowpea and maize at a combined density of 50,000 plants/ha intercropped with cotton at a density of 50,000 plants/ha. Maize provided a greater contribution to the land use efficiency than either cotton or cowpea. Cotton yield was highest in the spatial arrangement of single rows of cowpea and maize between single rows of cotton. For the two food crops, cowpea yield was highest in the spatial arrangements in which cowpea and maize were grown in different rows between rows of cotton, whereas maize yield was highest in the spatial arrangements in which cowpea and maize were grown in the same rows between rows of cotton. Cotton fiber quality was not influenced by spatial arrangement, cowpea/maize density, and cotton density. Number of cowpea pods was affected by spatial arrangement in a manner similar to cowpea yield. Number of maize ears increased as cowpea/maize density increased, whereas number of kernels/ear, weight of 100 kernels and length of kernel rows decreased as cowpea/maize density increased. Dry matter accumulation in leaves, stems, and fruits of cotton and cowpea was greatest in the spatial arrangements in which cowpea and maize were grown in different rows between rows of cotton. Weekly cotton growth rate increased as cotton density increased from 39 to 74 days after sowing.

Maize is one of the crops that is grown by most farmers in Zambia being the staple food for the majority of Zambians. However, despite the crop being so important, its production is dependent on climatic conditions. This means that any change in climate can affect the production either negatively or positively. This research therefore, focused on determining how the change in temperature and rainfall affect maize production on the Copper belt, Eastern, Lusaka and Southern provinces of Zambia and investigate the main adaptation measures implemented by both the government and non-governmental sectors. Also, assess through the review of National Agricultural Policy and action plans, how the government has documented issues of climate change. In order to obtain the needed data, interviews were conducted with different officials from both the government and non-governmental sectors. However, from the estimate of the impact of temperature and rainfall on maize production, the results did not show with any significance that either temperature or rainfall has effect on maize production. In fact, it was found that quantifying the effects of climate change on maize production is not easy due to difficulties in quantifying other factors that may also have large impact on maize production. It was therefore, not possible to conclude whether or to what extent climate change has effects on maize production. However from the interviews conducted, it was found that both the government and non-governmental sectors have introduced different activities in their programmes to ensure that farmers are food secure, though the ministry of agriculture has no policy document on how to handle the problem of climate change to address different issues of the sector. In fact, most offices in the ministry do not have much documented information on climate change which could also be seen from the review of National Agricultural Policy and action plans where climate change issue has not been emphasized. Though both the Government and non-governmental sectors have implemented some adaptation measures, it cannot easily be concluded whether the implemented measures are adequate or not due to the fact that we are not sure of the expected effects in different parts of the country. Nevertheless, to enhance food security with or without adverse effects of climate change on maize production, it was recommended that members of staff at all levels under MACO should be trained in the area of climate change for them to have a wider understanding of the issue and work responsively and that much research should be done to open up the mind of the people and help policy makers make effective plans.

The role of individual soil microorganisms changes over the course of a plant's life - microorganisms that have no discernable role at one developmental stage may affect the plant later in its growth. Traditional analysis of the soil microbiome, which has focused principally on the relative abundances (RA) of individual organisms, may be incomplete, as underlying differences in population size cannot be addressed. We conducted a metagenomic analysis of soil microorganisms from various maize (Zea mays L.) fields at two depths, accompanied by crop yield components, to provide insight into influences of edaphic microbes on maize productivity under commercial maize production systems in Missouri. This study assesses the influence of fungi and bacteria, not only in terms of RA, but also in their estimated absolute abundances (EAA), derived by combining the results of Illumina HiSeq sequencing data and phospholipid fatty acid abundance data. Significant interactions were identified between maize yield components and soil microbes at critical developmental states. Most interactions between fungi and yield components were negative, with notable exceptions. Bacterial interactions were more complex, with most interactions during early ear development identified as positive, and most interactions during tasseling identified as negative. In addition to the effects that microbial populations have on yield, plant populations reciprocally changed the microbial community. Plant developmental state was the greatest predictor of bacteria, with the microbial communities present during the active growing season being most similar to each other, whereas the preplant microbiome and post-reproductive microbiome being most similar to each other. Fungal communities were primarily dependent on location.

Thesis (M.Sc (Plant Production)) --University of Limpopo, 2015
Information on the performance of the maize and pigeonpea intercropping system under dryland conditions of South Africa is scanty. The aim of this study was to determine the optimum P level and productivity of pigeonpea and maize under the dryland intercropping system. Five P rates (0, 15, 30, 45, and 60 kg P ha-1) were applied to both sole and pigeonpea intercropped with maize in a randomized complete block design with 4 replicates. Growth parameters and yield and yield attributes of pigeonpea and maize were measured to determine performance of both crops. There were significant differences in grain yield of pigeonpea as influenced by P rates in both seasons. Highest grain yields of 781 kg ha-1 during 2009/10 and 894 kg ha-1 during 2010/11 were obtained at P rate of 45 kg ha-1. Cropping system significantly influenced grain yield of pigeonpea in 2010/11 season with 37.1% higher pigeonpea grain yield from intercropped plots than in sole pigeonpea plots. There was 21.8% increase in grain yield of pigeonpea across two seasons as influenced by P rate. Maize grain yield showed little response to P rate only during the first season. However, highest maize grain yield of 1699 kg ha-1 was obtained at 60 kg P ha-1 during the 2009/10 season. Maize grain yield was only significantly influenced by cropping system during the 2010/11 season where sole plots achieved higher grain yield of 4148 kg ha-1 compared to 3297 kg ha-1 from intercrop plots. The results revealed that P application increased grain yield of pigeonpea significantly, especially in intercropped plots. The calculated total land equivalent ratio (LER) for the two crops gave positive and higher than one values, which suggests a favourable grain yield advantage for maize/pigeon pea intercrop.

The southern region of Mozambique is characterized by arid to semi-arid climatic conditions with soils of poor fertility and low water retention capacity. The rainfall season is from September to April. In some areas, the rain season accommodates two production cycles, which is augmented by extended or unexpected rains in May and June. Maize is the main crop in this region. The major limiting factors for maize production in the Chókwè District under rainfed agriculture are rainfall amount and its distribution and soil fertility. Water productivity in this region is very low. The Challenge Program on Water and Food (CPWF), for which the slogan was “more crop per drop”, has attempted to identify and address water productivity constraints throughout the Limpopo River Basin (LRB). This study considers the water productivity in dryland areas, assuming that yields may not be only limited by water, but also by soil fertility. The study was aimed at investigating the improvement of water productivity by correcting nutrient deficiencies and recommending strategies to mitigate these deficiencies. A field experiment was conducted at Chókwè Agrarian Research Centre with maize cultivar (cv. Matuba). Matuba was selected because of its high tolerance to drought. Treatments were based on the most limiting soil nutrients at the experimental site. Crop parameters measured included total dry matter, fractional interception of photosynthetically active radiation (FIPAR), leaf area and grain yield. In addition, the Soil Water Balance (SWB) model was used to simulate potential yields with no nutrient limitations. Results of this study illustrated that the application of N resulted in improvements in total dry matter yield, leaf area index (LAI), FIPAR and water use efficiency (WUE). Application of both N and P improved the grain yield, leaf area duration (LAD) and WUE. SWB model simulations indicate that in only 1 out of 5 years in Chókwè District, the simulated yields were not higher compared to actual yields (0.2 - 1 ton ha-1). In conclusion, grain yield improvements are expected if nutrition is kept at optimum levels. This implies that in most years dryland yields are in fact nutrient limited and better nutrition can be used as a strategy to improve water productivity (WP) and grain yield
Dissertation (MSc Agric)--University of Pretoria, 2012.
gm2014
Plant Production and Soil Science
unrestricted

Field experiments were conducted on an Alfisol in the semi-arid tropics of northern Australia to investigate nitrogen (N) cycling in the leucaena (Leucaena leucocephala) alley cropping system. This is a farming system in which maize (Zea mays L.) is grown in alleys formed by leucaena hedgerows spaced 4.5 metres apart. Mineralization of N from Ieucaena (prunings) and maize residues was studied under field conditions. Response of maize growth to addition of N fertilizer and plant residues was evaluated both in field plot and microplot experiments. The fate of fertilizer N and leucaena N was examined over four consecutive seasons. The decomposition (loss of mass) of dry, cut 15N-labelled leucaena residues differed from that of intact fresh leucaena prunings in the first cropping season although no difference was detected after one year. At the end of one cropping season, 3 months after application, 58-72% of 15N-labelled leucaena had decomposed compared to only 34-36% of fresh leucaena prunings. Similar trends occurred at 20 and 52 days after application. The extent of decomposition of fresh leucaena prunings (28-33%) was similar at two loading rates (2.4 and 4.7 t DM ha -1) by 3 months after addition. About 72% of young 15N labelled maize residues was decomposed by 3 months after addition in the presence of fresh leucaena prunings. Decomposition of 15N-labelled leucaena residues and unlabelled fresh prunings was 91% and 88% respectively 14 months after addition. After 2 years the corresponding values were 96% and 94%. When N content of the recovered residues was taken into account, the values were 95% and 94% after 14 months, and the same (97%) after 2 years. Maize yield and N uptake were significantly increased following addition of either unlabelled fresh leucaena residues or 15N-labelled thy Ieucaena residues. Application of N ferilizer produced a thither increase in the presence of the residues. The maize yield and N uptake with the 15N-labelled leucaena were not different from those with the unlabelled residues. There was a significant positive interaction between N fertilizer and leucaena prunings which increased maize production. Addition of maize residues decreased the yield and N uptake of maize compared with that obtained in the presence of N fertilizer at 40 kg N ha~1 and leucaena residues (2.4 t DM ha-1). There was a marked residual benefit of N fertilizer applied in the first season at 36 kgN hat in the presence of leucaena prunings on the second maize crop yield and N uptake, but not on the third crop. However, a significant residual benefit of leucaena prunings added in the first season was found in DM yield and N uptake of the second and third maize crop. The short-term fate of 15N applied in plant residues was examined during two separate cropping seasons. By 20 days after application of separate 15N-labelled leucaena leaves, stems and petioles, 3-9% of the added 15N could be found in maize plants, 33-49% was in surface residues, 36-48% in the 2 m soil proffle and 0.3-22% unaccounted for. In a separate experiment when leucaena components were not separated, 5% of 15N applied in leucaena residues was taken up by maize 52 days after addition, 45% was in residues, 25% was in soil and 25% was unaccounted for. Jn another experiment, maize recovered 6% of added leucaena 15N after 2 months, 39% remained in residues, 28% was in soil and 27% was not recovered. Incorporation of 15N-labelled leucaena residues in the soil did not increase recoveiy of leucaena 15N by maize compared with placement of the residues on the soil surface. By the end of one cropping season (3 months after application), 9% of added 15N was recovered by maize from 15N-labelled leucaena. There was a similar 15N recoveiy from 15N-labelled maize residues applied as mulch at 1.7 t DM ha1 together with unlabelled leucaena prunings at 2.4 t DM ha ~. In both cases, 30-32% of added 15N was detected in soil, 28% in residues, and 31-34% apparently lost. The short-term fate of fertilizer 15N was different from that of 15N added in plant residues. In a 52-day experiment, maize recovered 65-79% of fertilizer 15N applied at low rates (6.1 and 12.2 kg N ha -1) in the presence of leucaena prunings, 21-34% was present in soil, and less than 1% was not recovered. By 2 months after application, recoveiy of fertilizer 15N by maize was 41% from N fertilizer added at 80 kg N ha -1, 35% from N fertilizer at 40 kg N ha -1 in the presence of leucaena prunings, and 24% from N fertilizer at 40 kg N ha -1 in the presence of maize residues and leucaena prunings. The corresponding deficits (unaccounted-for 15N) were 37%, 38% and 47% respectively. A small but significant amount of the fertilizer 15N was present in the unlabelled leucaena residues (3%) and in the mixture of unlabelled leucaena and maize residues (7%) present on the soil surface. However, application of the plant residues did not affect recoveiy of the fertilizer 15N in soil (21-24%). When N fertilizer was applied at 40 kg N hi1 in the presence of leucaena prunings, 43% of fertilizer 15N was recovered by maize at the end of cropping season, 20% in soil, 2% in residues, and 35% unaccounted for. The long-term fate of fertilizer 15N was compared with that of leucaena 15N in an experiment over four cropping seasons. In the first season, maize tops recovered 50% of the fertilizer 15N but only 4% of the leucaena 15N. In the second, third and fourth seasons, maize (tops + roots) recovered 0.7%, 0.4% and 0.3% of the initial fertilizer 15N compared with 2.6%, 1.8% and 1.4% of the initial leucaena 15N. In the second, third and fourth seasons, recovery of the initial fertilizer 15N (12-14%) in soil was much lower than that of the initial leucaena 15N (38-40%). There was no further loss of the fertilizer 15N after the first season. However, the cumulative 15N deficit for the leucaena 1N in the first two seasons was 50%--thissuggested an additional loss of 23% since the end of the first season. There was no further loss of 15N from either residual fertilizer 15N or residual leucaena 15N in the third and fourth seasons. In conclusion, application of leucaena prunings could substantially increase maize yield and N uptake although some supplementary N fertilizer may be required to achieve maximum crop yield. Maize recovered only a small amount of added leucaena N in the first year. Most of the leucaena residue N was present in the soil and remaining residues after one season. This residue N would be gradually available for plant uptake by subsequent crops. Of course, annual additions of leucaena prunings would appreciably increase the pool of available N over time. Thus, application of leucaena prunings could substantially improve soil fertility in the long term.

Mestrado em Engenharia Agronómica - Instituto Superior de Agronomia
The Northern leaf blight (NLB) caused by Exserohilum turcicum is one of the maize key diseases in all regions of production. In this dissertation, the susceptibility of four maize cultivars to reference isolates of E. turcicum was established under controlled conditions and the grain yield of the same cultivars evaluated and submitted to six treatments. Four treatments were engaged with fungicides (carbendazim+flusilazol or tebuconazol), one with NPK fertilizer and the sixth as a control. Field trials were conducted in Odemira and Coimbra, both places with known endemic presence of NLB in recent years. The susceptibility of cultivars to E. turcicum was evaluated with the Pioneer scale “Scoring Northern Leaf Blight” and the grain yield determined as 1000 grains weight and as specific weight. In the inoculation trials all cultivars showed the same level of susceptibility. The Coimbra trial didn‟t show any incidents of NLB. In the Odemira tests significant differences in disease severity were registered amongst cultivars and between treatments. The lower disease severity was recorded in the PR34P88 cultivar and in the treatment with two applications of tebuconazol. The treatments also led to significant differences in specific weight and 1000 grains weight. The grain yield varied significantly depending on the location and the cultivar

Field experiments were conducted on an Alfisol in the semi-arid tropics of northern Australia to investigate nitrogen (N) cycling in the leucaena (Leucaena leucocephala) alley cropping system. This is a farming system in which maize (Zea mays L.) is grown in alleys formed by leucaena hedgerows spaced 4.5 metres apart. Mineralization of N from Ieucaena (prunings) and maize residues was studied under field conditions. Response of maize growth to addition of N fertilizer and plant residues was evaluated both in field plot and microplot experiments. The fate of fertilizer N and leucaena N was examined over four consecutive seasons. The decomposition (loss of mass) of dry, cut 15N-labelled leucaena residues differed from that of intact fresh leucaena prunings in the first cropping season although no difference was detected after one year. At the end of one cropping season, 3 months after application, 58-72% of 15N-labelled leucaena had decomposed compared to only 34-36% of fresh leucaena prunings. Similar trends occurred at 20 and 52 days after application. The extent of decomposition of fresh leucaena prunings (28-33%) was similar at two loading rates (2.4 and 4.7 t DM ha -1) by 3 months after addition. About 72% of young 15N labled maize residues was decomposed by 3 months after addition in the presence of fresh leucaena prunings. Decomposition of 15N-labelled leucaena residues and unlabelled fresh prunings was 91% and 88% respectively 14 months after addition. After 2 years the corresponding values were 96% and 94%. When N content of the recovered residues was taken into account, the values were 95% and 94% after 14 months, and the same (97%) after 2 years. Maize yield and N uptake were significantly increased following addition of either unlabelled fresh leucaena residues or 15N-labelled thy Ieucaena residues. Application of N ferilizer produced a thither increase in the presence of the residues. The maize yield and N uptake with the 15N-labelled leucaena were not different from those with the unlabelled residues. There was a significant positive interaction between N fertilizer and leucaena prunings which increased maize production. Addition of maize residues decreased the yield and N uptake of maize compared with that obtained in the presence of N fertilizer at 40 kg N ha~1 and leucaena residues (2.4 t DM ha-1). There was a marked residual benefit of N fertilizer applied in the first season at 36 kgN hat in the presence of leucaena prunings on the second maize crop yield and N uptake, but not on the third crop. However, a significant residual benefit of leucaena prunings added in the first season was found in DM yield and N uptake of the second and third maize crop. The short-term fate of 15N applied in plant residues was examined during two separate cropping seasons. By 20 days after application of separate 15N-labelled leucaena leaves, stems and petioles, 3-9% of the added 15N could be found in maize plants, 33-49% was in surface residues, 36-48% in the 2 m soil proffle and 0.3-22% unaccounted for. In a separate experiment when leucaena components were not separated, 5% of 15N applied in leucaena residues was taken up by maize 52 days after addition, 45% was in residues, 25% was in soil and 25% was unaccounted for. Jn another experiment, maize recovered 6% of added leucaena 15N after 2 months, 39% remained in residues, 28% was in soil and 27% was not recovered. Incorporation of 15N-labelled leucaena residues in the soil did not increase recoveiy of leucaena 15N by maize compared with placement of the residues on the soil surface. By the end of one cropping season (3 months after application), 9% of added 15N was recovered by maize from 15N-labelled leucaena. There was a similar 15N recoveiy from 15N-labelled maize residues applied as mulch at 1.7 t DM ha1 together with unlabelled leucaena prunings at 2.4 t DM ha ~. In both cases, 30-32% of added 15N was detected in soil, 28% in residues, and 31-34% apparently lost. The short-term fate of fertilizer 15N was different from that of 15N added in plant residues. In a 52-day experiment, maize recovered 65-79% of fertilizer 15N applied at low rates (6.1 and 12.2 kg N ha -1) in the presence of leucaena prunings, 21-34% was present in soil, and less than 1% was not recovered. By 2 months after application, recoveiy of fertilizer 15N by maize was 41% from N fertilizer added at 80 kg N ha -1, 35% from N fertilizer at 40 kg N ha -1 in the presence of leucaena prunings, and 24% from N fertilizer at 40 kg N ha -1 in the presence of maize residues and leucaena prunings. The corresponding deficits (unaccounted-for 15N) were 37%, 38% and 47% respectively. A small but significant amount of the fertilizer 15N was present in the unlabelled leucaena residues (3%) and in the mixture of unlabelled leucaena and maize residues (7%) present on the soil surface. However, application of the plant residues did not affect recoveiy of the fertilizer 15N in soil (21-24%). When N fertilizer was applied at 40 kg N hi1 in the presence of leucaena prunings, 43% of fertilizer 15N was recovered by maize at the end of cropping season, 20% in soil, 2% in residues, and 35% unaccounted for. The long-term fate of fertilizer 15N was compared with that of leucaena 15N in an experiment over four cropping seasons. In the first season, maize tops recovered 50% of the fertilizer 15N but only 4% of the leucaena 15N. In the second, third and fourth seasons, maize (tops + roots) recovered 0.7%, 0.4% and 0.3% of the initial fertilizer 15N compared with 2.6%, 1.8% and 1.4% of the initial leucaena 15N. In the second, third and fourth seasons, recovery of the initial fertilizer 15N (12-14%) in soil was much lower than that of the initial leucaena 15N (38-40%). There was no further loss of the fertilizer 15N after the first season. However, the cumulative 15N deficit for the leucaena 1N in the first two seasons was 50%--thissuggested an additional loss of 23% since the end of the first season. There was no further loss of 15N from either residual fertilizer 15N or residual leucaena 15N in the third and fourth seasons. In conclusion, application of leucaena prunings could substantially increase maize yield and N uptake although some supplementary N fertilizer may be required to achieve maximum crop yield. Maize recovered only a small amount of added leucaena N in the first year. Most of the leucaena residue N was present in the soil and remaining residues after one season. This residue N would be gradually available for plant uptake by subsequent crops. Of course, annual additions of leucaena prunings would appreciably increase the pool of available N over time. Thus, application of leucaena prunings could substantially improve soil fertility in the long term.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Division of Australian Environmental Studies
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The potential for improved fertilizer nitrogen (N) use efficiency (NUE) and yield in winter wheat (Triticum aestivum L.) and maize (Zea mays L.) was tested using a new, controlled release urea formaldehyde polymer (UFP). This polymer was compared with conventional aqueous urea-ammonium nitrate (UAN) [(NH2)2CO?NH4NO3] fertilizer during a two-year field experiment in North Carolina from 2004 to 2006. The crops were grown on three soils: Candor (sandy, siliceous, thermic Grossarenic Kandiudult), Portsmouth (fine-loamy over sandy or sandy-skeletal, mixed, semiactive, thermic Typic Umbraquult) and Cape Fear (fine, mixed, semiactive, thermic Typic Umbraquult). The sandy soil was irrigated as needed to avoid drought stress. Treatments were N source (UAN and UFP) and N rate (0, 50, 78, 106, 134, 162, and 190 kg N ha-1 or 0, 45, 70, 95, 120, 145, and 170 lb ac-1 for wheat and 0, 39, 78, 118, 157, 196, and 235 kg N ha-1 or 0, 35, 70, 105, 140, 175, and 210 lb ac-1 for maize) arranged as randomized complete blocks with four replications. The UAN and UFP were applied as a split application for wheat, while maize received UFP at planting and split UAN. Timing of the materials was determined either by label (UFP) or prior experimental experience (UAN). Harvest biomass, grain, and mid-season soil sampling were performed to assess N availability. For both crops, UAN performed statistically similar to or better than UFP at both sites with regards to yields and NUE. Also, soil sampling and incubation results showed no consistent difference between N sources, implying the slow release properties of the UFP were not seen under the site and laboratory conditions. The release time for both sources at both sites was approximately 14 days (2 weeks). Since the cost of UFP is substantially greater than UAN and form did not significantly affect yield, UFP may not be as economical as UAN, depending on pricing of the different fertilizers.

Improved soil water conservation has become an important subject in semi-arid areas due to low and erratic rainfall which is often combined with higher temperatures to provide unsuitable conditions for successful crop productivity. Dryland agriculture remains vulnerable to yield losses in these areas. This calls for implementation of conservation agricultural practices that would improve dryland maize productivity. An on-station field trial was started in 2007 at Zeekoegat experimental farm (24 kilometers north of Pretoria), to establish the effect of different conservation agriculture practices on soil and plant properties. The experimental lay-out was a split-plot randomized complete block design, replicated three times, with each replicate split into two tillage systems (whole plots) and then each whole plot (reduced tillage (RT) and conventional tillage (CT)) was subdivided into 12 treatments (two fertilizer levels x 6 cropping patterns). The present study explored the impacts of different tillage practices, cropping patterns and fertilization levels on soil water content, soil temperature and dryland maize productivity during the 2010/11 and 2011/12 growing seasons. To improve the quality of soil water content (SWC) data, the effect of correction for concretions on soil bulk density and the relationship between volumetric soil water content (SWC) vs neutron water meter (NWM) count ratios was also investigated. Corrections for concretions on soil bulk density did not improve NWM calibrations in this study. In all seasons, significantly higher mean SWC was found under RT treatment than in CT at all depths except at 0-300 mm. For example, during the 2010/11 growing season, SWC under RT was 1.32 % and 1.10 % higher than CT for the 300 – 1350 mm and 0 – 1350 mm soil profiles, respectively. The mean weekly SWC was consistently higher for RT throughout both the growing seasons. Significantly higher SWC was also found under monoculture at all soil depths (except at 0-300 mm during 2011/12) compared to treatments under intercropping. For example, during 2010/11, at 0-300mm, SWC under maize monoculture was 1.72 % higher than under intercropping. The maximum and minimum soil temperatures were significantly higher at 100 and 400 mm soil depths under CT than under RT during 2010/11. During 2011/12, significantly higher minimum soil temperatures at 100 mm depth and lower temperature differences (maximum – minimum soil temperatures) at 400 mm depth were observed under intercropping. Despite the higher SWC and reduced soil temperature under RT, the maize seeds emergence rate was lower and plant stand was reduced. This is attributed to other factors associated with RT systems such as increased soil penetration resistance which often leads to poor root development. The lower soil temperatures under RT were generally within the range that would not be expected to inhibit growth and uptake of nutrients. Slower growth under RT resulted in lower biomass and grain yield. Plants that received high fertilizer rates grew more vigorously than plants under lower fertilizer levels when water was not a limiting factor, but produced lower grain yield due to water shortage in March, especially in 2011/12. The harvest index was therefore lower for treatments that received high fertilizer levels. Maize biomass under monoculture x low fertilizer level was significantly lower compared to other fertilizer x cropping pattern treatments. Maize plant growth under intercropping was improved throughout the seasons, which led to significantly higher grain yield than under maize monoculture. It is therefore recommended that farmers in dryland areas take the advantage of intercropping maize with legumes to obtain higher maize productivity. Further research should focus on investigating the possibility of roots restrictions occurring under RT conditions and under various environmental and soil conditions.
Dissertation (MScAgric)--University of Pretoria, 2014.
lk2014
Plant Production and Soil Science
MScAgric
Unrestricted

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The increment in plant density is an alternative to maximize solar radiation interception and to increase maize grain yield. However, it can also reduce the crop photosynthetic activity and limit its efficiency to convert carbohydrates to grain production. Increases in maize hybrid s tolerance to crowding have been reported in different production areas around the world. Two traits that may contribute to this feature are the slower leaf senescence during grain filling and the higher uniformity in plant growth and development during the crop cycle. This work was carried out aiming to quantify the effects of plant population increment on the leaf area, grain yield and the variation coefficient of agronomic traits of maize cultivars with contrasting genetic variability. The trial was set in Lages, SC, Brazil. A randomized block experimental design disposed in split-plots was used. Three cultivars were evaluated in the main plot: an open-pollinated variety (Fortuna), a double-cross hybrid (Ag 303) and a single-cross hybrid (P30F53). Five plant populations were tested in the split-plot: 25,000, 50,000, 75,000, 100,000, and 125,000 plants ha-1. The experiment was sowed on 10-26-2005, with a row spacing of 0.70 m. When the crop had four expanded leaves, 10 plants of each split-plot that were in the same growth stage were labeled. These plants were used to measure leaf area and to follow the crop growth, determining the variation coefficient of leaf area, growth stage and plant height. These variables were estimated 10 times, at the growth stages of V4, V8, V12, V16, R1 (silking) and 14, 28, 42, 56 and 70 days after silking. After harvesting, the variation coefficient and grain production per plant were determined based on the 10 selected plants. In addition to that, grain production and yield components were determined. The data were submitted to the variance analysis by the F test, at the 5.0% significance level (P<0.05). The means were compared by the Tukey s test (P<0.05), by polynomial regression and linear correlation. The response of grain yield to increment in plant population was quadratic, regardless of cultivar. Grain yield of the singlecross hybrid (SCH) was higher and more responsive to increase in plant density than grain yield of the double-cross hybrid (DCH) and the open-pollinated variety (OPV). The plant densities that optimized grain yield were 86,665 plants ha-1, 53,044 plants ha-1 and 85,000 plants ha-1 for the SCH, DCH and OPV, respectively. The SCH presented higher leaf area values than the other cultivars 56 days after silking, when plant populations greater than 50,000 plants ha-1 were used. The highest variation coefficient value for grain production per plant was registered at 125,000 plants ha-1 and the lowest at 25,000 plants ha-1. The SCH presented smaller variation coefficient than the DCH and OPV for plant height and leaf area at silking, and for grain yield per plant. The higher morphologic uniformity of the SCH probably contributed to reduce intra-specific competition for water, light and nutrients, establishing a stronger sink after flowering. The SCH greater demand for photosynthetic products possibly favored the maintenance of leaf activity for a higer period, delaying senescence. Therefore, the slower leaf senescence and the more uniform plant growth contributed to the SCH higher grain yield and to the higher productivity differences between the SCH and the other two cultivars in the highest plant densities (75,000, 100,000 e 125,000 plants ha-1)
O incremento na densidade de plantas é uma forma de maximizar a interceptação da radiação solar e o rendimento de grãos do milho. Contudo, ele também pode reduzir a atividade fotossintética da planta e a eficiência de conversão dos fotoassimilados à produção de grãos. Aumentos na tolerância de híbridos de milho ao adensamento têm sido reportados em diferentes regiões produtoras no mundo. Duas características que podem contribuir para isto são a senescência foliar mais lenta no enchimento de grãos e a maior uniformidade no crescimento e desenvolvimento das plantas durante o ciclo da cultura. Este trabalho foi conduzido com os objetivos de quantificar o efeito do incremento da população de plantas sobre a área foliar, o rendimento de grãos e o coeficiente de variação de características agronômicas de cultivares de milho com bases genéticas contrastantes. O experimento foi conduzido no município de Lages-SC. O delineamento experimental utilizado foi o de blocos casualizados dispostos em parcelas subdivididas. Na parcela principal foram testadas três cultivares de milho: uma variedade de polinização aberta (Fortuna), um híbrido duplo (Ag303) e um híbrido simples (P30F53). Cinco populações de plantas foram avaliadas nas subparcelas: 25.000, 50.000, 75.000, 100.000 e 125.000 plantas ha-1. O experimento foi implantado no dia 26 de outubro de 2005, com espaçamento entre linhas de 0,70 m. Quando a cultura estava com quatro folhas expandidas, marcou-se 10 plantas de cada subparcela que estivessem no mesmo estádio fenológico. Estas plantas foram utilizadas para as avaliações de área foliar, bem como para o acompanhamento do crescimento, determinando-se o coeficiente de variação para área foliar, estádio fenológico e estatura de planta. Estas variáveis foram avaliadas 10 vezes, nos estádios V4, V8, V12, V16, R1 (espigamento) e aos 14, 28, 42, 56 e 70 dias após o espigamento. Após a colheita, foram determinados o coeficiente de variação e a produção de grãos por planta, nas 10 plantas selecionadas. Além disso, determinou-se a produção de grãos na área útil, bem como os componentes do rendimento. Os dados foram submetidos à análise de variância pelo teste F, ao nível de significância de 5% (P<0,05). As médias foram analisadas pelo teste de Tukey, a 5% de probabilidade de erro (P<0,05), por regressão polinomial e por correlação linear. A reposta do rendimento de grãos das três cultivares ao incremento na densidade de plantas foi quadrática. O rendimento de grãos do híbrido simples (HS) foi maior e mais responsivo ao incremento na população de plantas do que o híbrido duplo (HD) e da variedade de polinização aberta (VPA). As populações que otimizaram o rendimento de grãos foram de 86.665 plantas ha-1, 53.044 plantas ha-1 e 85.000 plantas ha-1 para o HS, HD e VPA, respectivamente. O HS apresentou maior valor de área foliar do que as demais cultivares aos 56 dias após o espigamento, nas densidades superiores a 50.000 plantas ha-1. Os maiores coeficientes de variação para produção de grãos por planta foram obtidos na densidade de 125.000 plantas ha-1 e os menores na de 25.000 plantas ha-1. O HS apresentou menor coeficiente de variação do que o HD e a VPA para estatura de planta e área foliar no espigamento, bem como para produção de grãos por planta. As maiores uniformidades morfológica e fenológica do HS provavelmente contribuiu para reduzir a competição intra-específica por água, luz e nutrientes, favorecendo o estabelecimento de um dreno mais forte logo após a floração. A maior demanda por fotoassimilados do HS possivelmente favoreceu a manutenção da atividade fotossintética das folhas por um período mais longo, retardando a senescência foliar. Portanto, a senescência foliar mais lenta e o desenvolvimento uniforme das plantas contribuíram para o maior rendimento de grãos do HS e para as maiores diferenças de produtividade registradas entre o HS e o HD e a VPA nas densidades mais altas (75.000, 100.000 e 125.000 plantas ha-1)

Intensive tillage and monoculture cropping practices reduce soil C accumulation hence increasing soil vulnerability to chemical, physical and biological degradation. This study focussed on enhancing biomass production of wheat and oat winter cover crops as a means of increasing C sequestration in the low organic C soils of the central part of Eastern Cape Province. The specific objectives were (i) to evaluate the short-term effects of no till and cereal-fallow based crop rotations on; soil organic matter related parameters, pH and electrical conductivity, (ii) soil bulk density, water retention and aggregate stability, (iii) soil microbial biomass C and N, mineralizable N, soil respiration, and dehydrogenase enzyme activity, (iv) grain yield, soil nutrient concentration (N, P and K) and their uptake by maize, and (v) to identify soil parameters with high sensitivity to tillage under maize-fallow-maize, maize-wheat-maize and maize-oat-maize rotational cover cropping practices. The experiment was laid out as a split-plot arrangement in a randomized complete block design with 4 replicates. Tillage treatments (CT and NT) were applied on the main plots which measured 8 × 18 m while crop rotation treatments were applied in the subplots which measured 8 × 6 m. The rotation treatments were maize-fallow-maize (MFM), maize-wheat-maize (MWM) and maize-oat-maize (MOM). Weed control in NT plots involved preplant application of glyphosate to control mainly the grass weeds while post emergence weed management was done using Atrazine (485 atrazine and 15 g l-1 triazines). Initial weed control in CT plots was achieved through ploughing to a depth of 20 cm followed by disking while post emergence weed iii management was done by hand hoeing. Soil parameters measured were; (i) particulate organic matter (POM), soil organic carbon (SOC), total nitrogen (TN), pH and electrical conductivity (EC), (ii) soil bulk density (b), moisture at field capacity (FC), aggregate mean weight diameter (MWD) determined by fast wetting (FW), slow wetting (SW), mechanical breakdown by shaking (MB) and the stability index (SI), (iii) soil microbial biomass C (MBC) and N (MBN), mineralizable N (MN), soil respiration (SR), and dehydrogenase enzyme activity (DHEA). No-till increased POM and TN compared to CT in Lenye and Burnshill, respectively. The MWM and the MOM rotations increased TN relative to the MFM rotation in Lenye. The MWM and MOM rotations enhanced SOC relative to MFM in all sampled soil depths at Burnshill and similar observations were made under MOM rotation in the 5-20 cm depth in Lenye. The MWM and MOM rotations tended to depress soil pH relative to the MFM rotation in both sampled soil depths in Lenye while NT reduced soil pH relative to CT on the surface soil layer in Burnshill. Soil EC and pH varied with depth across tillage practices but both parameters remained within the ideal range for successful crop production over the study period. Soil stability index (SI) and aggregate MWD determined by FW, SW and MB were higher in Lenye compared to Burnshill. The MOM rotation enhanced the SI relative to MFM and MWM rotations at both sites. Scanning electron microscope (SEM) showed that more organic C was incorporated into the soil under NT and MOM rotation compared to CT and MFM rotation which had few organic coatings on the soil particles. Microbial properties varied with plant biomass input as influenced by tillage and type of rotational cover crop at both sites. Like in other past studies, NT showed higher levels of MBC, MBN, NM and SR at the soil surface layer compared to CT in Burnshill. No till increased MN iv relative to CT in both sampled soil depths in Lenye and resulted in higher DHEA compared to CT in Burnshill. The MOM rotation increased MBC, MBN, MN relative to MFM rotation especially within surface soil layer. Similar observations were made with respect to MN and SR in both sampled soil layers at Lenye. By contrast, the DHEA was higher under the MFM relative to the MWM and MOM rotations in Lenye but similar under the MFM and MOM rotations in Burnshill. Maize grain yield was not affected by both tillage and crop rotations but varied with cropping season. Comparable grain yields observed under the two tillage practices with similar fertilizer application rates indicated the advantage of NT over CT in saving on labour costs in maize production without compromising yields. High plant biomass retention under NT relative to CT contributed to high soil N and P levels under the former compared to the latter tillage practice especially on soil surface layer at both study sites. Principal component analysis (PCA) revealed that soil chemical and biological parameters closely linked to organic matter, namely SOC, MN, MBC and MBN showed the highest sensitivity to tillage and crop rotation treatments. Soil aggregate MWD determined by SW and b were the physical parameters which were highly altered by agronomic management practice. The MWM and MOM rotations were clustered together and clearly separated from the MFM rotation and this observed trend only applied to the 0-5 and 5-20 cm depths in Lenye site only. No till, MWM and MOM rotations enhanced POM, SOC and TN relative to CT and MFM rotation suggesting these practices have greater potential to improve soil chemical properties compared to intensive tillage and maize monoculture based production practices. Reduced soil b under MOM rotation and improved SI under NT compared to MFM and CT, respectively v indicate that these practices have the potential to improve degraded soils. Although not significantly different, NT values for MBC, MBN, MN, SR and DHEA were higher compared to CT indicating the potential of the practice to improve soil biotic activity relative to conventional tillage practices. No till enhanced surface soil nitrate N and extractable P compared to CT at both sites revealing the long-term potential of NT in improving the supply of these essential plant nutrients compared to CT. Principal component analysis showed that SOC, MN, K, P, MBC, MBN, soil aggregate MWD determined by SW and b were the most sensitive parameters to tillage and crop rotations. Therefore, these parameters could constitute the minimum data set for assessments of the impact of selected CA practices on soil quality attributes.

Doctor of Philosophy
Department of Agronomy
P. V. Vara Prasad
Leguminous cover crops systems have been envisaged as a critical component of sustainable agriculture due to their potential to increase soil productivity through cycling of carbon (C) and nitrogen (N) in agricultural systems. The objectives of this study were to evaluate the performance of leguminous summer cover crops; cowpea [Vigna unguiculata (L.) Walp.], pigeon pea [Cajanus cajan (L.) Millsp], sunn hemp (Crotalaria juncea L.) and double-cropped grain crops; grain sorghum [Sorghum bicolor (L.) Moench] and soybean [Glycine max (L.) Merr.] after winter wheat (Triticum aestivum L.) and to determine the effects of these crops and varying N rates in the cropping system on nitrous oxide (N[subscript]2O) emissions, growth and yield of succeeding grain sorghum and maize (Zea mays L.) crop, soil aggregation, aggregate-associated C, and N. Field and laboratory studies were conducted for two years. The cover crops and double-cropped grain crops were planted immediately after winter wheat harvest. The cover crops were terminated at the beginning of flowering. Nitrogen fertilizer (urea 46% N) rates of 0, 45, 90, 135, and 180 kg N ha[superscript]-1 were applied to grain sorghum or maize in fallow plots. Pigeon pea and grain sorghum had more C accumulation than cowpea, sunn hemp and double-cropped soybean. Pigeon pea and cowpea had more N uptake than sunn hemp and the double-cropped grain crops. Fallow with N fertilizer application produced significantly greater N[subscript]2O emissions than all the cover crops systems. Nitrous oxide emissions were relatively similar in the various cover crop systems and fallow with 0 kg N ha[superscript]-1. Grain yield of sorghum and maize in all the cover crop and double cropped soybean systems was similar to that in the fallow with 45 kg N ha[superscript]-1. Both grain sorghum and maize in the double-cropped soybean system and fallow with 90 kg N ha[superscript]-1 or 135 kg N ha[superscript]-1 gave profitable economic net returns over the years. The double-cropped grain sorghum system increased aggregate-associated C and whole soil total C, and all the cover crop and the double-cropped soybean systems increased aggregate-associated N and soil N pools. Inclusion of leguminous cover crops without N fertilizer application reduced N[subscript]2O emissions and provided additional C accumulation and N uptake, contributing to increased grain yield of the following cereal grain crop.

Thesis (M.Sc. (Agronomy )) --University of Limpopo, 2007
Intercropping is the growing of two or more crops simultaneously on the same field, and it is a common traditional practice among resource-poor farmers throughout the Limpopo Province of South Africa. Field studies were conducted at two locations in the province namely, the University of Limpopo experimental farm at Syferkuil, and a farmer’s field at Dalmada during the 2002/2003 growing season, to determine patterns of nodulation in cowpea and lablab varieties under sole culture and in an intercropping system with maize, variety SNK2147 and also to assess biomass accumulation and grain yielding abilities of the component crops in the system. The experiments were established as a randomized complete block design with three replications at each location. Treatments examined were sole maize, two cowpea cultivars: Bechuana white and Glenda; two lablab cultivars, Rongai and Common. The legumes were intercropped alternately within 90 cm inter-row spacing of maize, thus creating a distance of 45 cm between the maize and the legume rows. Cropping system had no effect on cowpea grain yield at Syferkuil, but at Dalmada cowpea yield was reduced. Maize grain yield was significantly affected by the cropping system at both Syferkuil and Dalmada. At both locations, the yields of all the intercropped maize were lower than those of the sole crop maize. The dry matter production of different cropping systems was generally similar during the different sampling dates.
the National Research Foundation,and the Gauteng Department of Agriculture Conservation and Environment

Early yield prediction of a maize crop is important for planning and policy decisions. Many countries, including South Africa use the conventional techniques of data collection for maize crop monitoring and yield estimation which are based on ground-based visits and reports. These methods are subjective, very costly and time consuming. Empirical models have been developed using weather data. These are also associated with a number of problems due to the limited spatial distribution of weather stations. Efforts are being made to improve the accuracy and timeliness of yield prediction methods. With the launching of satellites, satellite data are being used for maize crop monitoring and yield prediction. Many studies have revealed that there is a correlation between remotely sensed data (vegetation indices) and crop yields. The satellite based approaches are less expensive, save time, data acquisition covers large areas and can be used to estimate maize grain yields before harvest. This study applied Landsat 8 satellite based vegetation indices, Normalized Difference Vegetation Index (NDVI), Soil Adjusted Vegetation Index (SAVI) and Moisture Stress Index (MSI) to predict maize crop yield. These vegetation indices were derived at different growth stages. The investigation was carried out in the Kopanong Local Municipality of the Free State Province, South Africa. Ground-based data (actual harvested maize yields) was collected from Department of Agriculture, Forestry and Fisheries (DAFF). Satellite images were acquired from Geoterra Image (Pty) Ltd and weather data was from the South African Weather Service (SAWS). Multilinear regression approaches were used to relate yields to the remotely sensed indices and meteorological data was used during the development of yield estimation models. The results showed that there are significant correlations between remotely sensed vegetation indices and maize grain yield; up to 63 percent maize yield was predicted from vegetation indices. The study also revealed that NDVI and SAVI are better yield predictors at reproductive growth stages of maize and MSI is a better index to estimate maize yield at both vegetative and reproductive growth stages. The results obtained in this study indicated that maize grain yields can be estimated using satellite indices at different maize growth stages.

Sendo o cereal mais produzido no mundo e em larga expansão, os sistemas de produção de milho são altamente complexos e sua produção é diretamente dependente de fatores ligados tanto ao clima local quanto ao manejo da cultura. Para auxiliar na determinação tanto dos patamares produtivos de milho quanto quantificar o impacto causado por condições adversas tanto de clima quanto de manejo, pode-se lançar mão do uso de modelos de simulação de culturas. Para que os modelos possam ser devidamente aplicados, uma base solida de dados meteorológicos deve ser consistida, a fim de alimentar esses modelos. Nesse sentido, o presente estudo teve como objetivos: i) avaliar dois sistemas de obtenção de dados meteorológicos, o NASA-POWER e o DailyGridded, comparando-os com dados medidos em estações de solo; ii) calibrar, testar e combinar os modelos de simulação MZA-FAO, CSM DSSAT Ceres-Maize e APSIM-Maize, a fim de estimar as produtividades potenciais e atingíveis do milho no Brasil; iii) avaliar o impacto na produtividade causado pelo posicionamento da semeadura em diferentes tipos de solo; iv) desenvolver e avaliar um sistema de previsão de safra baseado em modelos de simulação; v) mapear as produtividades potencial, atingível e real do milho no Brasil, identificando regiões mais aptas ao cultivo e vi) determinar e mapear as quebras de produtividade, ou yield gaps (YG) da cultura do milho no Brasil. Comparando os dados climáticos dos sistemas em ponto de grade com os dados de estações meteorológicas de superfície, na escala diária, encontrou-se boa correlação entre as variáveis meteorológicas, inclusive para a chuva, com R2 da ordem de 0,58 e índice d = 0,85. O desempenho da combinação dos modelos ao final da calibração e ajuste se mostrou superior ao desempenho dos modelos individuais, com erros absolutos médios relativamente baixos (EAM = 627 kg ha-1) e com boa precisão (R2 = 0,62) e ótima acurácia (d = 1,00). Durante a avaliação da influência das épocas de semeadura e do tipo de solo no patamar produtivo do milho, observou-se que esse varia de acordo com a região estudada e apresenta seus valores máximos e com menores riscos à produção quando a semeaduras coincidem com o início do período de chuvas do local. O sistema de previsão de safra, baseado em modelos de simulação de cultura teve seu melhor desempenho simulando produtividades de milho semeados no início da safra e no final da safrinha, sendo capaz de prever de forma satisfatória a produtividade com até 25 dias antes da colheita. Para o estudo dos YGs, 152 locais foram avaliados e suas produtividades potenciais e atingíveis foram comparadas às produtividades reais, obtidas junto ao IBGE. Os maiores YGs referentes ao déficit hídrico se deram em solos arenosos e durante os meses de outono e inverno, usualmente mais secos na maioria das regiões brasileiras, atingindo valores de quebra superiores a 12000 kg ha-1. Quanto ao YG causado pelo manejo, esse foi maior nas regiões menos tecnificadas, como na região Norte e na Nordeste, apresentando valores superiores a 6000 kg ha-1. Já as regiões mais tecnificadas e tradicionais na produção de milho, como a região Sul e a Centro-Oeste, os YGs referentes ao manejo foram inferiores a 3500 kg ha-1 na maioria dos casos.
Maize is the most important cereal cultivated in the world, being its production system very complex and its productivity directly affected by climatic and crop management factors. In order to quantify the impacts caused by water and crop management deficits on maize yield, the use of crop simulation models is very useful. For properly apply these models, a solid basis of meteorological data is required. In this sense, the present study had as objectives: i) to evaluate two meteorological gridded data, NASA-POWER and DailyGridded, by comparing them with measured data from surface stations; (ii) to calibrate, evaluate and combine the MZA-FAO, CSM DSSAT Ceres-Maize and APSIM-Maize simulation models to estimate the maize potential and attainable yields in Brazil; iii) to evaluate the impact caused by the different sowing dates and soil types on maize yield; iv) to develop and evaluate a crop forecasting system based on crop simulation models and climatological data; v) to map the potential and the attainable maize yields in Brazil, identifying the most suitable regions for cultivation, and vi) to determine and map maize yields and yield gaps (YG) in Brazil. Comparing the gridded climatic data with observed ones, on a daily basis, a good agreement was found for all weather variables, including rainfall, with R2 = 0.58 and d = 0,85. The performances of the combination of the models at the end of the calibration and evaluation phases were better than those obtained with the individual models, with relatively low mean absolute error (EAM = 627 kg ha-1) and with good precision (R2 = 0.62) and accuracy (d = 1.00). During the evaluation of different sowing dates and soil types on maize yield, it was observed that this variable depends on the region and presents the maximum values and, consequently, the minimum risk during the sowings in the beginning of the rainy season of each site. The crop forecasting system, based on crop simulation models, had its best performance for simulating maize yields when the sowings were performed at the beginning of the main season and at the end of the second season, when it was able to predict yield satisfactorily 25 days before harvest. For the YG analysis, 152 sites were assessed and their potential and attainable yields were compared to the actual yields reported by IBGE. The highest YGs caused by water deficit occurred for sandy soils and during the autumn and winter months, usually dry in most of Brazilian regions, reaching values above 12000 kg ha-1. For YG caused by crop management, the values were higher in the less technified regions, such as in the North and Northeast regions, with values above 6000 kg ha-1. In contrast, more traditional maize production regions, such as the South and Center-West, presented YG caused by crop management, lower than 3500 kg ha-1 in most cases.

付記する学位プログラム名: グローバル生存学大学院連携プログラム
Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第21465号
農博第2308号
新制||農||1064(附属図書館)
学位論文||H31||N5160(農学部図書室)
京都大学大学院農学研究科地域環境科学専攻
(主査)教授 舟川 晋也, 教授 間藤 徹, 教授 縄田 栄治
学位規則第4条第1項該当

Modern maize hybrids exhibit higher yields, increased biomass production, stress tolerance and greater nitrogen (N) use efficiency. Increased biomass accumulation can influence nutrient uptake and lead to increased nutrient removal. Hybrids were tested at seeding rates (SR) of 74000 (low) and 148000 (supraoptimal) plants ha-1 and at N rates of 0 (deficient) and 390 (non-limiting) kg N ha-1. Plants were sampled at V7, V14, R3, R5 and R6 and separated into vegetative and reproductive fractions for determination of dry matter and N accumulation. Grain yield was harvested at R6. The high SR and high N treatment combination resulted in greatest biomass accumulation, crop growth rates, and N accumulation per hectare in both vegetative and grain tissues. The high SR and high N combination maximized grain yield at 20.6 Mg ha-1, essentially through an increase in kernels ha-1. High SR decreased kernel weight, even with high N. At the higher plant densities resulting from the high SR, however, average utilization of available N was enhanced. The results have implications for improved management practices under high input systems and providing insight to growers who incorporate variable seed and N rates.