Tesis sobre el tema "Rainfall yield"

Rain-fed agriculture is extremely important in sub-Saharan Africa, thus the ability to forecast and monitor regional crop yields throughout the growing season would be of enormous benefit to decision makers. Of equal importance to be able to assign a measure of uncertainty to the forecast, especially considering that many predictions are made in the context of a complex climate and sparse meteorological and agricultural observations. This work investigates these issues in the context of an operational updating regional crop yield forecast, concentrating in particular on a case study forecasting Ethiopian maize. Part 1 of the work presented a detailed discussion of Ethiopia' s climate and agricultural systems. As real-time ground based weather observations are sparse in Africa, Part 2 contains an investigation into remotely sensed satellite rainfall estimates. A daily TAMSAT calibration and the geostatistical process of sequential simulation were used to create a spatially correlated ensemble of Meteosat-derived rainfall estimates. The ensemble mean was evaluated as a daily deterministic rainfall product and was found to be as good as or better than other products applied in the same region. A validation of the full ensemble showed that they realistically estimated Ethiopian rainfall fields that agreed both with observed spatial correlations and input pixel level statistics. Part 3 of the work includes a discussion on regional crop simulation modelling and presents a new parameterisation of the GLAM crop simulation model for tropical maize. GLAMMAIZE was then driven using individual members of the satellite ensemble; this was shown to exhibit the correct sensitivities to climate inputs and performed reasonably against yield observations. Finally, Part 4 presented a new method of creating stochastic spatially and temporally correlated rainfall fields. This 'regional weather generator' was tested using a case study on Ethiopian April rainfall and a detailed discussion was included about future development plans.

Limited research has been conducted and uncertainty exists regarding sugarcane response to water stress during different development phases. This information is necessary to optimize the allocation of limited irrigation water for sugarcane production. The objective of this study was to understand and quantify the response of crop water use (CWU), canopy development, stalk elongation, biomass accumulation and partitioning, and sugarcane yield to mild water stress, imposed through deficit drip irrigation, during different development phases. A field experiment consisting of a plant and first ratoon crop of cultivar N49 was conducted near Komatipoort. For the three water stress treatments, available soil water (ASW) was maintained between 30 and 60% of capacity during the tillering phase (TP), stalk elongation phase (SEP) and through both phases. ASW was maintained above 60% of capacity in the well-watered control and during periods when stress was not intended. Rainfall prevented water stress from developing in the TP of the plant crop. In the ratoon crop, 72% less irrigation was applied in the TP, resulting in 50 days of stress (ASW<50%). This did not affect stalk population but reduced CWU by 13%, shortened stalks by 21% and affected the canopy by reducing green leaf number (GLN) and green leaf area index (GLAI). Relieving the stress during SEP allowed the crop to re-establish its canopy, capture adequate photosynthetically active radiation (PAR) and restore rates of photo-assimilation (as suggested by CWU) and stalk elongation to support rapid biomass production. This restoration of plant processes allowed the ratoon crop to attain a cane and stalk dry biomass (SDM) yield that was only 9 and 11% lower (statistically insignificant), respectively, than the well-watered control at lodging (crop age of 286 days). During the SEP of the plant and ratoon crop, 42 and 85% less irrigation was applied, resulting in the crops experiencing 74 and 39 days of stress and using 7 and 8% less water, respectively. This did not affect stalk population or the crop canopy, but reduced stalk height by about 6 and 14% in the plant and ratoon crops, respectively. In both crops, shorter stalks and a negatively affected CWU which reduced photo-assimilate production, reduced cane yield by 14 and 10% (statically insignificant) and SDM yield by 15 and 5% (statistically insignificant), in the plant and ratoon crops respectively. © University of Pretoria iv Deficit irrigation throughout the TP and SEP of the ratoon crop reduced irrigation amount by 74%, resulting in 110 days of stress and reducing CWU by 16% and stalk height by 14%. PAR capture was reduced through reduced GLAI. This resulted in a significant reduction of 15% in cane yield. SDM yield was reduced by 17%, although this was not statistically significant. Stalk sucrose content was not influenced by deficit irrigation but was rather dependent on the duration of the drying-off period prior to harvest. Sucrose yields were therefore largely determined by SDM. Results suggest that the soil water potential (SWP) measured at 0.25 and 0.40 m depths, halfway between drip emitters within a plant or ratoon crop, can drop to about -40 kPa before irrigation is applied, without sacrificing cane or sucrose yield. Lastly, a ratoon crop can rapidly recover from stress during the TP, provided that the SWP during SEP is maintained above -40 kPa.
Dissertation (MSc Agric)--University of Pretoria, 2013.
gm2014
Plant Production and Soil Science
unrestricted

Cotton (Gossipium hiristum, L) is a warm season perennial with indeterminant growth habit. In 1995, 42,500 and 300,000 hectares were grown in Virginia and North Carolina, respectively. Soil physical and chemical properties may limit cotton yields. The objective of this study was to; 1) determine influences of soil physical and chemical properties on yield, 2) validate existing preharvest yield estimators, and 3) determine the effect of subsoiling and/or subsurface liming on cotton development and root growth. Two hundred sites were sampled across the Coastal Plain of Virginia and North Carolina to a depth of 92 cm representing 5 major soil series. Soil samples were analyzed for selected physical and chemical properties from each horizon. Boll and plant counts were obtained while harvesting a 3-meter length of row at each site to determine yield for the 1996 and 1997 growing season. Cotton was grown in the greenhouse on 30 cm diameter cores of a soil with low subsoil pH and a hard pan to determine the effects of subsoiling and/or subsurface liming. Ninety days after planting, the cotton plants were harvested and the above ground biomass and rootmass were analyzed. Physical and chemical properties explained 52% of yield variability in 1996 and 27% in 1997. Physical and chemical properties that were significant to yield were surface bulk density, available water holding capacity, depth of the water table and Bt horizon, Mg, K, Ca, and Al content. Soil analysis for nutrient status at depths up to 45 cm were better indicators of cotton yield. Subsoiling with or without subsurface liming increased rooting depth over the untreated check. The subsurface liming reached first flower 11 days prior to the other treatments. The additional period for flowering and boll set in Virginia and North Carolina could increase potential yield.
Ph. D.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
O objetivo desta pesquisa é analisar a variabilidade das chuvas e a produtividade da soja em regiões produtoras no Brasil, Estados Unidos e Índia. A partir de um estudo comparativo e amparado pelas análises climatológicas que envolvem técnicas estatísticas e cartográficas, buscou-se compreender os arranjos regionais particulares a cada realidade. Configurada e considerada sob as possibilidades e formas desiguais de acesso à técnica e ao manejo necessário para minimizar os efeitos adversos e negativos/positivos da variabilidade, considera-se que essa heterogeneidade dá o caráter de maior ou menor susceptibilidade as quebras ou déficits agrícolas. Espera-se contextualizar a realidade regional em função da observação dos diferentes arranjos regionais produzidos diferentemente conforme a história e da política internacional em conexões globais, para tanto, foi elaborada a parte de fundamentação teórica tratando temas contemporâneos da geopolítica, da globalização, do conceito de região e da importância de se realizar um estudo comparado. Foram coletados dados de produtividade de soja e de precipitação e temperatura de quatro regiões. A primeira delas localiza-se no sul do Brasil e é constituída pela região noroeste do Rio Grande do Sul, a segunda localiza-se no centro oeste do Brasil, mais especificamente o norte do Mato Grosso, a terceira é nos Estados Unidos e constitui o noroeste do Estado de Ohio, e a quarta situa-se na região central e mais agrícola da Índia, o oeste do estado de Madhya Pradesh. Cada região apresenta diferentes características e especificidades quanto a história, cultura, padrões, crenças, estruturas econômicas, etc., mas detém uma característica em comum, a presença da soja, fator determinante para realizar uma pesquisa comparativa. Os resultados mostraram maior variação dos totais anuais de produtividade de soja no noroeste do Rio Grande do Sul, Ohio e Madhya Pradesh e menor variação, indicando maior homogeneidade no norte do Mato Grosso. O Mato Grosso, juntamente com Ohio são os dois maiores produtores, com valores anuais alcançando, em alguns casos, 3,800 kg/ha. O Rio Grande do Sul, neste contexto, se torna intermediário, com marcada variação anual tanto entre os totais regionais, quanto entre os municípios. A região indiana mostra valores baixos se comparado às demais regiões, porém com certa homogeneidade dos dados – baixa variação. A variabilidade das chuvas também foi marcada no Rio Grande do Sul, Ohio e com menor intensidade em Madhya Pradesh e norte do Mato Grosso. Apesar das análises nas escalas anuais indicar bons resultados, foi a partir da redução para a escala mensal que foi possível medir com maior precisão os níveis de correlação entre a chuva e a produtividade de soja. Para o sul do Brasil, 90% dos resultados do total de 42 testes realizados mostraram uma correlação estatisticamente significativa (para valores de p entre 0,001 e 0,03), principalmente para os meses de janeiro e fevereiro. Nos Estados Unidos, os resultados apresentaram correlações positivas com valores de p entre 0,028 e 0,042 em julho e agosto e negativos em maio. Estes mesmos testes não foram significativos no norte do Mato Grosso e na região indiana. No sul do Brasil, os resultados estatisticamente positivos correspondem aos principais períodos de desenvolvimento da soja, onde as necessidades de água são maiores: os meses de janeiro e fevereiro correspondem à floração, ao desenvolvimento e ao enchimento das vagens, um período que requer uma boa distribuição de precipitação (o que explica o grande número de correlações positivas). Ao mesmo tempo, nos Estados Unidos, os resultados indicam uma maior dependência entre os rendimentos da soja e as chuvas que ocorrem em julho e agosto, o que corresponde também ao período mais importante para o desenvolvimento fenológico da cultura nesta região. Os resultados integram e contribuem para pesquisas relacionadas à climatologia numa escala global, e aos estudos dos impactos regionais das mudanças climáticas, e temas da geopolítica no contexto atual (estratégicas), relacionado à produção de alimentos. Em síntese, a tese representou uma correlação entre a realidade climática geográfica (chuva e vulnerabilidade agrícola) a partir do contexto regional de cada ponto escolhido.
This research main goal is to analyze the rainfall variability and soybean yield in producing regions in Brazil, India and United States. The study sought to understand the specific regional arrangements based on a comparative study supported by climatological analyzes involving statistical and cartographic techniques. Configured and considered under different and unequal technique access forms and required management to minimize variability’ positive/negative adverse effects, the research considers this heterogeneity gives greater or lesser susceptibility to agricultural breaks or deficits. Different regional arrangements are produced differently according to history and global connection international politics. Theoretical basis was elaborated dealing with contemporary geopolitics issues such as globalization, concept of region and comparative study. 4-regions soybean yield, precipitation and temperature data were collected. The first region corresponds to Southern Brazil, specifically Rio Grande do Sul northwest, and the second is placed on Brazil’s Middle-West, at northern Mato Grosso state. The third region is located at United States, in northwest Ohio state, and the fourth one represents the most agricultural region of India: western Madhya Pradesh state. Strong annual soybean yield variability was found in Rio Grande do Sul, Ohio and Madhya Pradesh, with less variation and strong homogeneity in Mato Grosso. Also, Mato Grosso and Ohio are the largest producers, with annual values reaching 3,800kg/ha, followed by Rio Grande do Sul, affected by seasonality. The Indian region shows the lowest values although has a strong data homogeneity (less variation). Annual rainfall variability was well marked in Rio Grande do Sul and Ohio, with less intensity in Madhya Pradesh and northern Mato Grosso state. However, monthly data allows to reach better correlations between soybean yield and rainfall. 90% of 42 correlation tests showed statistical significance (p-value between 0.001 and 0.03) for southern Brazil, principally in January and February. For Ohio, positive correlations (p-value between 0,028 and 0.042) were found in July and August, and negative correlations were found in May. The first result corresponds to main soybean development period in Brazil, with more water needs: January and February correspond to flowering and pods’ filling and development period, that requires a satisfactory precipitation distribution (which explains the substantial number of positive correlations). At the same time, in United States the results indicate more dependence between soybean yield and July and August rainfall, most important months to phenological development at this region. The results increase climatological research related to climate at global scale, and the climate change regional impacts. Also contributes to geopolitics issues at current context (strategies), related to food production. The thesis presents correlation between the geographical-climatic reality (rainfall and agricultural vulnerability) from regional context of each selected point.
FAPESP: 2014/01071-1
FAPESP: 2015/18063-4
FAPESP: 2016/24271-1

Projected increasing temperatures and reduced summer precipitation in the UK raises questions about the sustainability of aspects of the agriculture industry and food security. This study investigates the potential impact of precipitation changes on sugar beet yield in Eastern England. Observations of precipitation was examined for the period 1971-2000 and the expected changes in precipitation were investigated using seven CMIP5 climate models for the historical phase (1971-2000) and RCP45 and RCP85 future scenarios (2021-2050). Three out of the seven models were found to show good agreement with observations but the MOHC ensemble mean was the closest to the observed means and was used for further precipitation analyses. Statistical analysis of the future precipitation changes were performed using the Met Office Hadley Centre (MOHC) model focused on changes between the historical phase and RCP45 and RCP85. Results showed a consistent and significant reduction in annual May-October precipitation under future scenarios. The study then investigated the impact of reduced future precipitation changes on sugar beet yield by applying controlled watering regimes informed by the CMIP5 projections to sugar beet plants in a greenhouse experiment over two seasons - the use of CMIP5 projections in this way is a first. In the first experiment carried out in 2014, a climatological watering regime (i.e. where the total seasonal rainfall for the different scenarios was applied in equal and regular watering events) was applied to the plants, which meant a 16% reduction in precipitation in the "future" category relative to a "control" category. Analysis of the yields indicated a statistically significant reduction in mean tuber wet mass: mean of 360g for the control and 319g for the future (p-value 0.03). This implies a potential yield reduction of 11% by 2050. In the second experiment carried out in 2015, a "realistic distribution" watering regime (i.e. where the total seasonal rainfall is applied in a series of watering events that reflect the analysed sizes and distribution of rainfall events in the different categories), this meant a reduction in precipitation in the months of June (-15.6%), July (-7.7%) and August (-3.7%). This resulted in statistically significant reduction in mean tuber wet mass between control (153g) and RCP85 (113g) with a p-value of 0.01. This implies a reduction of 26% in future yields under RCP85 by 2050. Results in this thesis further show how changes and variation in precipitation are intertwined with changes in soil moisture and yield of sugar beet plants. The findings will enable UK sugar beet farmers to identify potential areas of challenges in order to adapt their management practices to ensure maximum crop yield in future growing seasons. Moreover, from a global perspective, the findings here are also broadly applicable to a variety of agricultural crops in different parts of the world, where changes in yield may have important consequences to food security and food prices.

Large scale land clearing for livestock grazing has accelerated the soil loss and sediment delivery from Great Barrier Reef (GBR) catchments in Australia. Areas with low ground cover are known to generate large runoff volumes at a small scale (<100m2). However, the spatial effect of ground cover variation on runoff generation and soil loss is not well studied in the large catchment (~ ≥1 km2). Thus, it is essential to characterise the spatial distribution of ground cover to evaluate the effect of variation in cover on runoff in the GBR catchments. Despite recognising the potential effect of ground cover variation in runoff generation and soil loss, the current GBR eWater Source Catchment Modelling Framework uses lumped rainfall-runoff models that consider only rainfall and potential evapotranspiration as input variables. In addition, the Revised Universal Soil Loss Equation (RUSLE), which considers only effect of rainfall as rainfall-runoff erosivity has been used to estimate hillslope soil loss. However, the effect of runoff on rainfall-runoff erosivity and on hillslope soil loss is not studied well in Australia, particularly in Queensland. To evaluate the effects of ground cover variation on runoff and soil loss, this research was conducted in Central Queensland in 32 sub-catchments of Burnett-Mary Basin (35.84 - 231.17 km2), three experimental Brigalow catchments (11.7 – 16.8 ha) and Springvale catchment (9.6 ha) and Nogoa catchment (13,880 km2) in the Fitzroy basin and Weany Creek (Virginia Park) catchment (11.9 ha) in the Burdekin basin. Except the Burnett-Mary sub catchments, the measured runoff and sediment data were available for all the other catchments for the selected period. This study has three objectives: (1) to model the spatial distribution of vegetation cover in a parameter-efficient manner in grazing land, (2) to compare and evaluate the performance of Revised USLE and Modified USLE models for soil loss prediction, and (3) to integrate the ground cover variation with rainfall-runoff models for catchment scale runoff prediction. To address the first objective, the beta distribution was used to characterise cover variation in space at the sub-catchment scale. Three methods were used to test the appropriateness of the beta distribution: (i) visual goodness-of-fit assessment and Kolmogorov–Smirnov (K-S) test; (ii) the fractional area with cover ≤53%; and (iii) estimated runoff amount for a given rainfall amount for the fractional area with 3 | P a g e cover ≤53%. It was concluded that the two-parameter beta distribution is a parameter efficient method to characterise the spatial variation of cover and to evaluate the effect of cover variation on runoff in grazing catchments. In the second objective, the sediment yield changes due to the conversion of brigalow forest to cropping and grazing was assessed and the potential contributing factors to sediment yield were identified. It also evaluated the comparative performance of the Revised Universal Soil Loss Equation (RUSLE) and the Modified Universal Soil Loss Equation (MUSLE) in predicting the sediment yield from the three BCS catchments. The study supports applying the MUSLE model, which considers runoff (Q) and peak runoff rate (Qp) in BCS for improved sediment yield prediction. This work has been extended to three grazed catchments of Fitzroy and Burdekin basins to compare and evaluate the performance of RUSLE and MUSLE models for predicting soil loss/sediment yield for grazing catchments. The MUSLE models performed better as compared to the RUSLE model for all three catchments. Compared to the RUSLE model, the MUSLE1 model with factors Q and Qp, was able to predict sediment yield for Weany creek and Brigalow catchment and the MUSLE2 with factors EI30, Q and Qp performed well for Springvale and Brigalow catchment. The calibrated soil erodibility factor (K) was found to be 14%, 24%, and 60% higher for Springvale, Brigalow, and Weany Creek catchments, respectively, compared to the K-factor from the Australian Soil Resource Information System (ASRIS). This study recommends using the MUSLE model to improve sediment yield prediction from hillslope grazing lands in Australia. In the third objective, the influence of the spatial and temporal variation of cover on runoff using a conceptual framework to integrate the cover variation with lumped rainfall-runoff models for the Nogoa catchment (13,880 km2) was investigated. Preliminary findings of this study show that modified SimHyd cannot provide improved runoff estimation when the spatial and temporal variation of ground cover is taken into consideration. Use of an alternative approach, i.e., SCS Curve Number (CN) method for individual storm events shows that when the combined effect of rainfall and ground cover on CN is considered, the groundcover affect CN negatively, i.e., the lower the cover, the larger the value of CN, hence the higher the storm runoff amount for the same amount of rainfall. 4 | P a g e The exponent for ground cover is different from zero comparing to rainfall. Therefore, it can be concluded that though the modified SimHyd model wouldn’t provide the improved estimation of runoff, however, the alternative approach i.e., CN method shows that ground cover significantly affects runoff and cannot be ignored for the Nogoa catchment. Overall, this study highlights the need for an improved understanding of the effect of the spatial distribution of ground cover on runoff and sediment delivery from large grazing catchments, with the main findings as follows: (1) the spatial distribution of ground cover can be efficiently described using beta distribution, (2) runoff and peak runoff rate are the major variables responsible for variations in sediment yield from grazing catchments, (3) the MUSLE model should be used for grazing catchments irrespective of the catchment size for improved prediction of sediment yield with some modifications to soil erodibility values, (4) the effect of change in ground cover on runoff was identified using the SCS-CN method, hence, an improvement in the current lumped hydrological modelling framework would be achieved with inclusion of spatial variability of ground cover in addition to rainfall and potential evapotranspiration as input to hydrological models and should be further tested and developed for dry catchments with low ground cover for improved simulation of runoff from grazing catchments.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text

A GIS-based method has been applied for assessing the spatial soil erosion risk and sediment yield in Mae Rim watershed, Northwest Thailand. The gross soil erosion in each watershed cell was estimated using the Revised Universal Soil Loss Equation (RUSLE) by thoroughly determining its various parameters. RUSLE results showed mean annual soil loss rate of 31 tonnes ha-1 yr-1, while the mean annual suspended sediment yield was 7.4 tonnes ha-1 yr-1. From the results of the spatial analysis between controlling factors and soil erosion, it indicated that bare land, field crop land and high steep slope were linked to extreme soil erosion (> 150 tonnes ha-1 yr-1). With respect to soil erosion under land use and rainfall change, it was revealed that the conversion from deciduous forest to field crop area has very serious implications for soil erosion in the Mae Rim watershed. Indeed, transition from forest to agriculture may lead to erosion increase despite reduced rainfall. The results obtained from analysing scenario sensitivities identify synergistic effects on soil erosion hazard if bare land, field crop land and rainfall erosivity are increased simultaneously in the future.

It is widely believed that Acacia karroo Hayne trees compete with and negatively affect the production of grasses in their immediate surroundings. This perception formed as a result of observations by farmers of their veld as well as some research. The complexity of plant interactions in different conditions required that research be done to better explain the extent of grass and tree interactions. In response to this need, the effect of a range of Acacia karroo densities on grass production was tested in areas of differing rainfall. Results emphasize the complexity of such plant interactions but highlight rainfall as influencing the effect of tree density on grass production and grass quality. Study sites were chosen with significant differences in tree density and rainfall and this was found to be concomitant with significant differences in grass yield and crude protein (p < 0.001). Grass yield (mass produced) was negatively correlated with tree density (p < 0.001) and was affected by rainfall. High tree density reduced grass yield at the lower rainfall sites, but a reduction in yield was only recorded during dry conditions in the higher rainfall areas. By contrast, the crude protein content of grasses was positively correlated to tree density (p < 0.001). However, as with yield, rainfall played an important part in the strength of the correlation. Soil properties such as temperature (-) (p = 0.011), phosphorus content (+) (p = 0.006), calcium concentration (+) (p = 0.005), acid saturation (-) (p = 0.018), and soil pH (+) (p = 0.008) were also significantly correlated to tree density. Tree density enriched the soil, subsequently benefitting grass quality. The study sites investigated, had different plant communities and environmental conditions with Cradock, Kubusi Drift and Kei Mouth having unique communities and conditions while Adelaide and Cathcart could not be separated in either. Cradock was the driest site and the vegetation was dominated by both grasses and karroid shrubs, differing in pattern and process from the other sites. The Kubusi Drift site had high tree densities, to the extent that the trees altered the grass species composition. The effects of rainfall on grass yield and quality exceeded that of community composition differences.

Accelerated soil erosion is one of the major threats to agricultural production in Ethiopia and the Harerge region is not exceptional. It is estimated that about 1.5 billion tones of soil is being eroded every year in Ethiopia. In the extreme cases, especially for the highlands, the rate of soil loss is estimated to reach up to 300 t ha-1yr-1 with an average of about 70 t ha -1yr-1 which is beyond any tolerable level. The government have made different attempts to avert the situation since 1975 through initiation of a massive program of soil conservation and rehabilitation of severely degraded lands. Despite considerable efforts, the achievements were far bellow expectations. This study was aimed at assessing the effect of some soil properties, rainfall intensity and slope gradients on surface sealing, soil erodibility, runoff and soil loss from selected sites in the Harerge region, eastern Ethiopia, using simulated rainfall. Soil loss was also estimated for the sites using Soil Loss Estimation Model for Southern Africa (SLEMSA) and the Universal soil Loss Equation (USLE). Moreover, the effectiveness of various rates and patterns of wheat residue mulching in controlling soil loss was also evaluated for one of the study sites, (i.e. Regosol of Alemaya University), under both rainfall simulation and field natural rainfall conditions. For most of the erosion parameters, the interaction among soil texture, slope gradient and rainfall intensity was significant. In general however, high rainfall intensity induced high runoff, sediment yield and splash. The effect of slope gradients on most of the erosion parameters was not significant as the slope length was too small to bring about a concentrated flow. The effect of soils dominated by any one of the three soil separates on the erosion parameters was largely dependent on rainfall intensity and slope gradient. The soils form the 15 different sites in Harerge showed different degrees of vulnerability to surface sealing, runoff and sediment yield. These differences were associated with various soil properties. Correlation of soil properties to the erosion parameters revealed that aggregate stability was the main factor that determined the susceptibility of soils to sealing, runoff and soil loss. This was in turn affected by organic carbon content, percent clay and exchangeable sodium percentage (ESP). Soils with relatively high ESP such as those at Babile (13.85) and Gelemso (7.18) were among the lowest in their aggregate stability (percent water stable aggregates of 0.25 –2.0mm diameter); and have highest runoff and sediment yield as compared to other soils in the study. Similarly, most of those soils with relatively low ESP, high organic carbon content (OC%) and high water stable aggregates such as Hamaressa, AU (Alemaya University) vertisol and AU regosol were among the least susceptible to sealing and interrill erosion. Nevertheless, some exceptions include soils like those of Hirna where high runoff was recorded whilst having relatively high OC%, low ESP and high water stable aggregates. Both the SLEMSA and USLE models were able to identify the erosion hazards for the study sites. Despite the differences in the procedures of the two models, significant correlation (r = 0.87) was observed between the values estimated by the two methods. Both models estimated higher soil loss for Gelemso, Babile, Karamara and Hamaressa. Soil loss was lower for Diredawa, AU-vertisol and AU-Alluvial all of which occur on a relatively low slope gradients. The high soil loss for Babile and Gelemso conforms with the relative soil erodibility values obtained under rainfall simulation suggesting that soil erodibility, among others, is the main factor contributing to high soil loss for these soils. The difference in the estimated soil losses for the different sites was a function of the interaction of the various factors involved. Though the laboratory soil erodibility values were low to medium for Hamaressa and Karamara, the estimated soil loss was higher owing to the field topographic situations such as high slope gradient. SLEMSA and USLE showed different degrees of sensitivities to their input variables for the conditions of the study sites. SLEMSA was highly sensitive to changes in rainfall kinetic energy (E) and soil erodibility (F) and less sensitive to the cover and slope length factors. The sensitivity of SLEMSA to changes in the cover factor was higher for areas having initially smaller percentage rainfall interception values. On the other hand, USLE was highly sensitive to slope gradient and less so to slope length as compared to the other input factors. The study on the various rates and application patterns of wheat residue on runoff and soil loss both in the laboratory rainfall simulation and under field natural rainfall conditions revealed that surface application of crop residue is more effective in reducing soil loss and runoff than incorporating the same amount of the residue into the soil. Likewise, for a particular residue application method, runoff and soil loss decreased with increasing application rate of the mulch. However, the difference was not significant between 4 Mg ha-1 and 8 Mg ha-1 wheat straw rates suggesting that the former can effectively control soil loss and can be used in areas where there is limitation of crop residues provided that other conditions are similar to that of the study site (AU Regosols). The effectiveness of lower rates of straw (i.e. less than 4 Mg ha-1 ) should also be studied. It should however be noted that the effectiveness of mulching in controlling soils loss and runoff could be different under various slope gradients, rainfall characteristics and cover types that were not covered in this study. Integrated soil and water conservation research is required to develop a comprehensive database for modelling various soil erosion parameters. Further research is therefore required on the effect of soil properties (with special emphasis to aggregate stability, clay mineralogy, exchangeable cations, soil texture and organic matter), types and rates of crop residues, cropping and tillage systems, mechanical and biological soil conservation measures on soil erosion and its conservation for a better estimation of the actual soil loss in the study sites. Copyright 2004, 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: Bobe, BW 2004, Evaluation of soil erosion in the Harerge region of Ethiopia using soil loss models, rainfall simulation and field trials, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-08022004-141533 / >
Thesis (PhD (Soil Science))--University of Pretoria, 2004.
Plant Production and Soil Science
unrestricted

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The influence of climatic variables on angular leaf spot of common bean (Phaseolus vulgaris L.) and the reaction of the causal agent Pseudocercospora griseola (Sacc.) Crous & Braun to the carbendazim fungicide were assessed in this study. A methodology for assessing the pathogen resistance to the carbendazim fungicide, of wide use in Brazilian agriculture, was developed at Embrapa Rice and Beans, in Santo Antônio de Goiás. The test was based on P. griseola conidia suspensions at concentrations of 103, 104 and 105 spores mL-1, fungicide concentrations of the at 1 ppm, 10 ppm and 100 ppm per mL-1at the presence of Alamar Blue dye. Alamar Blue is an indicator of cell activity, where the metabolism of viable cells corresponds to a higher dye reduction and a colorimetric reaction. The experimental results were assessed with the support a spectrophotometer to quantify the amount of reduced dye, and thus, to verify the pathogen’s resistance to the fungicide. The results demonstrated the feasibility of the method and greater resistance of the isolate Pg 669 to carbendazim in comparison to isolates Pg 410 and Pg 786. Furthermore, the recommended methodology consisted on fungicide at 100 ppm, 1 × 104 conidia mL-1and 40 hours of incubation at 25ºC. Another study considered the relationships between angular leaf spot severity, crop yield and climate variables to estimate the impacts of monthly rainfall and the El Niño Southern Oscillation (ENSO) phenomenon on the disease and yield losses in crops established in the spring/summer (November-February) or fall (February-May) season, in crops established in the spring/summer (November-February) or fall (February-May) season, in different Brazilian municipalities, between 2001 and 2010. The disease data was retrieved from experiments of value, cultivation and use (VCU), conducted by Embrapa and its partners, with the cultivars Pérola, BRS Grafite e BRS Requinte. These tests were carried out in a randomized block design with three replications. The results showed differences (p<0.05) between cultivars and between planting seasons. By means of regression analysis, an inversely proportional relationship between yield and disease severity was found. The principal components analysis, in turn, revealed that ENSO influences differently disease severity and crop yield according to the location of the experiments in the Brazilian states of Goiás, Paraná and Pernambuco. These results provide new evidences about the efficiency of commercially used fungicides for angular leaf spot management, demonstrate the impacts of the disease on a regional scale, and support predictive models of disease and risk assessments of climate change on the development of crops.
Este trabalho avaliou a influência de variáveis climáticas sobre a mancha angular do feijoeiro comum (Phaseolus vulgaris L.), e a reação de seu agente causal Pseudocercospora griseola (Sacc.) Crous & Braun ao fungicida carbendazim. Na Embrapa Arroz e Feijão (Santo Antônio de Goiás, GO) foi desenvolvida uma metodologia para avaliação da resistência do patógeno ao fungicida carbendazim, de amplo uso na agricultura brasileira. Foram avaliadas suspensões de conídios de P. griseola em concentrações de 103, 104 e 105 esporos mL-1 com concentrações do fungicida a 1 ppm, 10 ppm e 100 ppm mL-1, junto ao corante Alamar Blue. Este corante função é um indicador da atividade celular presente, onde maior a atividade celular corresponde a uma maior redução do corante, o que resulta em uma reação colorimétrica. A análise do experimento foi feita com o auxílio de um espectrofotômetro, para quantificar a quantidade de corante reduzida e assim verificar a resistência do patógeno ao fungicida testado. Os resultados demonstraram a viabilidade do método e a maior resistência do isolado Pg 669 ao carbendazim, em relação aos Pg 410 e Pg 786, e recomendação para estes ensaios com o fungicida a 100 ppm, 1 × 104 esporos mL- 1, 10 l de Alamar Blue em um intervalo de incubação ótimo de 40 horas a 25ºC. Em outro estudo, foi realizado um levantamento da severidade da mancha angular, da produtividade da cultura e de variáveis climáticas para se estimar os impactos da precipitação mensal e do fenômeno El-Niño Oscilação Sul (ENSO) sobre a doença e as perdas de rendimento nas safras das águas e da seca, em diferentes municípios brasileiros, entre 2001 e 2010. Os dados foram provenientes de ensaios de valoração, cultivo e uso (VCU), conduzidos pela Embrapa e seus parceiros, com as cultivares Pérola, BRS Grafite e BRS Requinte, na safra das águas (novembro-fevereiro) e, eventualmente, da seca (fevereiro-maio). A partir das análises realizadas foram observadas diferenças (p<0,05) entre as cultivares e entre as épocas de plantio. Por meio da análise de regressão, foi observada uma relação inversamente proporcional entre produtividade e severidade da doença. A análise de componentes principais, por sua vez, revelou que o fenômeno ENSO influencia diferentemente a severidade da doença e produtividade da cultura conforme a localização dos plantios nos estados de Goiás, Paraná e Pernambuco. Estes resultados fornecem novos subsídios sobre avaliar a eficiência dos fungicidas utilizados comercialmente para o manejo da mancha angular, demonstram dos impactos da doença em escala regional e subsidiam o desenvolvimento de modelos de previsão de doenças e avaliações de risco de mudanças climáticas sobre o desenvolvimento de cultivos do feijão comum

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
O objetivo geral foi quantificar e avaliar os principais processos hidrol?gicos, incluindo a produ??o de sedimentos, da Bacia Experimental de Aiuaba (BEA) para o per?odo de 2003-2007. A BEA, com ?rea de 12 km2, est? localizada no sert?o dos Inhamus em ?rea de conserva??o ambiental do bioma caatinga na Esta??o Ecol?gica (ESEC) de Aiuaba, Cear?, pertencente ? bacia do Alto Jaguaribe. Realizou-se caracteriza??o da fisiografia, medi??o de vari?veis hidrol?gicas, avalia??o de processos chuva-defl?vio na bacia hidrogr?fica e no reservat?rio que a controla. Conclui-se que: o processo de infiltra??o do a?ude da BEA (capacidade de 59.700 m3) ? relevante e da mesma ordem de grandeza da evapora??o; a recarga subterr?nea direta ao lago ? desprez?vel em rela??o ? evapora??o e ? infiltra??o; durante os eventos chuva-defl?vio a evapora??o, a infiltra??o e a recarga subterr?nea s?o desprez?veis em rela??o ao defl?vio afluente e ? precipita??o direta sobre o lago. Conclui-se, dos eventos chuva-defl?vio e produ??o de sedimentos, que: o coeficiente de runoff (CR) dos eventos ? extremamente baixo, sendo as l?minas d??gua escoadas menores que as l?minas interceptadas pela vegeta??o; o N?mero de Curva (CN) m?dio por evento foi 42, com m?ximo de 59 e m?nimo de 27; a produ??o de sedimentos apresentou valores entre 9 e 291 kg/km2 para eventos de 2006-2007, e m?dia de 97 kg/km2 por evento; o escoamento superficial ? ef?mero: o tempo de defl?vio foi somente 64% maior que o tempo da precipita??o por evento; as perdas elevadas no escoamento superficial ocorrem, em parte, por perdas em tr?nsito no riacho principal; a l?mina escoada na bacia do riacho secund?rio foi oito vezes maior que na bacia do riacho principal em 2007. Inferiu-se que o mecanismo de gera??o de defl?vio superficial predominante ? o hortoniano e que, se relevante, a contribui??o do escoamento subsuperficial deve ocorrer a uma profundidade menor que 15 cm. O CR m?dio anual da BEA foi 6,54% (m?ximo de 31,08% e m?nimo de 0,13%). No ano de 2004 a l?mina escoada na BEA foi 35 vezes maior que a soma das l?minas escoadas nos demais anos. Dos 1543 dias monitorados, em apenas 139 dias ocorreu escoamento (9%), sendo 28 dias de escoamento nos anos n?o-chuvosos (1,8%). A produ??o de sedimentos em 2007 foi cinco vezes maior que em 2006, e para o bi?nio 2006-07 o m?s de maior escoamento (abril de 2007) foi respons?vel por 71% da produ??o de sedimentos. Comparando-se o CR anual da BEA com outras bacias no rio Jaguaribe, a BEA foi uma das que apresentou menor coeficiente de runoff. Formulou-se a hip?tese de a BEA ser uma ?rea de recarga de aq??fero fraturado, que condiciona processos hidrol?gicos superficiais.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Areas susceptibility to water erosion and strong pressure of soil use, as in Southern Brazil, where there is cultivation of tobacco, are prone to degradation of the natural resources. The objective of this dissertation was to evaluate the unsustainability of the natural resources in a watershed under tobacco production, characterized by steep slopes, with intense agricultural exploration and to evaluate the processes related to soil erosion. The watershed is located in the district of Nova Boêmia, Agudo, RS. The watershed has an area of 332 ha, with is subdivided, in right left subbasin, by two streams, forming the main drainage of the Arroio Lino Friedlich, flowing to the Jacuí River. The evaluations were: 1. The evolution of soil use and management, and soil erosion from 2003 to 2005; 2. Physical and environmental factors affecting soil, namely rain erosivity, LS (slope length and steepness) of the Universal Soil Loss Equation, and watershed concentration time; 3. For the quantification of the sediment yield, samples of the suspended sediment were colleted during rain events in the year of 2005, in two control sections, using flow meters that quantified the water flow rate for subsequent determination of the flow and sediment concentration, through from specific rating curves; 4. The annual sediment yield estimation was made through sediment rating curves, using lineal and polynomial models. Precipitation data were obtained automatically from a meteorological station located in the center of the watershed and were used for the determination of rainfall erosivity. Several maps were generated, including classes of factor LS index of the USLE. The results showed that the agricultural areas are increasing and natural vegetation is decreasing. Under this rate, there would be no natural vegetation in 100 years. The concentration time of the watershed is of 12 minutes, meaning that in a short time the whole watershed contributes for the runoff, in accordance with the sudden increase of the water height in the creek. The hydro-sedimentologic components varied mainly with soil moisture, topographical characteristics and rainfall intensity and amount. Erosive rainfall occurred mainly in the second semester of the year, when the soil was also plowed. The right side drainage of the watershed contributed with 80% of the sediment yield and presented higher values of LS factor, more intense soil, presence of highways and gullies and smaller riparian zone. The polynomial model for the sediment rating curves had the best adjustment and was effective in estimating the annual sediment yield. Estimated soil erosion rates from cropland was 0.28 cm ha-1 year and from unpaved roads was 0.12 cm ha-1 year, which are greater than both soil formation and soil loss tolerance rates. These data indicate the unsustainable use of the soils for tobacco growth under current management practices.
Áreas vulneráveis em termos de suscetibilidade à erosão e a forte pressão de uso do solo, como na região Sul do Brasil onde há cultivo de fumo, propiciam a degradação do ambiente. O objetivo foi avaliar a (in)sustentabilidade de agroecossistemas intensamente explorados com a cultura do fumo numa pequena bacia hidrográfica rural de cabeceira com terras declivosas, solos rasos, com ênfase na erosão do solo. A bacia está localizada no distrito de Nova Boêmia, Agudo- RS. A área de captação da bacia corresponde a 332 ha e essa é subdividida, para este estudo, em lados direito (braço direito) e esquerdo (braço esquerdo), em função da rede de drenagem que possui dois córregos, que ao final da secção se juntam em apenas um, formando o braço principal do Arroio Lino Friedlich, afluente do Rio Jacuí. As avaliações foram: 1) quantificação das variáveis de uso e manejo do solo influenciadores da erosão do solo, nos anos de 2003 a 2005; 2) variáveis físico-ambientais influenciadores da erosão do solo, sendo elas a erosividade das chuvas, o fator LS (comprimento do declive L e grau do declive S) da Equação Universal de Perda de Solo, e o tempo de concentração da bacia; 3) medida da produção de sedimentos em suspensão e construção de hietogramas, hidrogramas e sedimentogramas de eventos chuvosos ocorridos no ano de 2005, em seções de controle localizadas no exutório da bacia nos braços esquerdo e principal, nos quais estavam presentes linígrafos que registraram, de forma automática, dados de altura de lâmina de água para posterior determinação da vazão e concentração de sedimentos, a partir de curvas-chave específicas; 4) estimativa da produção de sedimentos anual, a partir da construção de uma curva-chave, sendo avaliados dois modelos, o linear e o polinomial. Dados de precipitação foram obtidos automaticamente numa estação meteorológica situada no centro da bacia e serviram para a determinação do índice de erosividade da chuva. Diversos mapas foram confecionados, sendo um deles o mapa com as classes de fator de LS. Os resultados mostraram que as áreas de lavouras vêm aumentando no decorrer dos anos e, conseqüentemente, as de vegetação natural estão diminuindo. Em se continuando esse processo, em cem anos não mais haverá vegetação natural. O tempo de concentração da bacia é de 12 minutos, significando que num curto espaço de tempo toda a bacia passa a contribuir para o escoamento e confirmando o aumento súbito da altura de lâmina de água no riacho. As componentes hidrossedimentológicas variaram principalmente com a umidade do solo, características topográficas e da precipitação, intensidade e quantidade. Chuvas mais erosivas se situam no segundo semestre do ano, onde o solo estava revolvido pela ação das práticas de cultivo. O lado direito da bacia contribuiu com 80% da produção de sedimentos e apresentou valores mais elevados das classes do fator LS, maior uso antrópico do solo, presença de estradas e ravinas e menor zona ripária. O modelo polinomial para a obtenção da curva-chave de sedimentos teve o melhor ajuste e foi eficaz na estimativa da produção anual de sedimentos. A quantidade de solo erodida e estimada das áreas de lavouras foi de 0,28 cm ha-1 ano, enquanto que das áreas de estradas foi de 0,12 cm ha-1 ano. As perdas por erosão hídrica desses solos da bacia estão muito acima dos valores de suas taxas de formação e também das perdas de solo toleráveis. Isso indica a insustentabilidade perante o atual uso agrícola com a cultura do fumo.

La prévision de crues joue un rôle fondamental dans l’anticipation et la mise en œuvre de mesures visant à protéger les personnes et les biens. L’objectif de cette thèse est d’examiner notre capacité à améliorer la simulation et la prévision d’événements majeurs de crues soudaines en France. Premièrement, nous examinons les limites de l’approche globale de modélisation hydrologique et la contribution du modèle hydrologique semi-distribué GRSD, à maillage fin et au pas de temps horaire, à la simulation d’évènements majeurs de crue. Nous proposons une modification de la structure de ce modèle afin qu’il soit mieux adapté à reproduire la réponse des bassins versants aux fortes intensités de pluie. Une adaptation de la structure du modèle, basée sur le calcul du rendement de pluies, a abouti à l’introduction d’un nouveau paramètre et à la proposition d’un nouveau modèle (GRSDi) mieux capable de simuler la réponse hydrologique à des pluies intenses qui surviennent en automne. Deuxièmement, nous explorons comment une approche de prévision d’ensemble météorologique, combinée au modèle hydrologique semi-distribué, peut contribuer à mieux prévoir les évènements de crues rapides, l’amplitude et l’instant d’occurrence des débits de pointe, que ce soit sur des bassins jaugés ou non-jaugés. Les résultats ont permis d’identifier, du point de vue hydrologique, les forces et faiblesses des produits proposés. Les travaux menés constituent un pas en avant vers l’utilisation de modèles hydrologiques conceptuels, continus et semi-distribués, dans le cadre de la prévision de crues majeures et rapides en contexte méditerranéen
Flood forecasting plays a fundamental role in anticipating and implementing measures to protect lives and property. The objective of this thesis is to investigate our ability to improve the simulation and forecasting of major flash flood events in France. First, we analyse the limitations of the lumped hydrological modelling approach, and how the contribution of the semi-distributed hydrological model GRSD, with fine mesh and hourly time step, to improve the simulation of major flood events. We also propose a modification of the structure of the model, in order to make it better suited to reproducing the response of the catchments to high rainfall intensities. An adaptation of the model structure, based on the calculation of the production rate function, resulted in the introduction of a new parameter and the proposal of a new model (GRSDi) capable of better simulating the hydrological response to heavy rains that occur in autumn, after a dry summer period. Second, we explore the ability of a meteorological ensemble prediction approach, combined with the semi-distributed hydrological model, to better predict flash flood events, the amplitude and the time of occurrence of peak flows, whether in gauged or ungauged basins. The results made it possible to identify, from a hydrological point of view, the strengths and weaknesses of the products evaluated. The work carried out constitutes a step forward towards the use of conceptual, continuous and semi-distributed hydrological models for the forecasting of major flood events and flash floods in the Mediterranean context

This thesis assesses the relationships between the El Niño-Southern Oscillation (ENSO), rainfall and South African commercial winter wheat yields from 1974 - 2000. The analysis is through a combination of the Pearson's product moment correlation coefficient and an assessment of the magnitude and consistency of rainfall and wheat anomalies in the year of, and the year following warm (El Niño) and cold (La Niña) ENSO events. The ENSO - rainfall relationship is analysed on timescales from 1 - 24 months and this study finds that there are more unusually dry and unusually wet months during El Niño events than during La Niña episodes (where dry and wet months are <75°/o and over 25~·'0 more than the 1921 - 2000 mean, respectively) and these conditions are consistently found in some rainfall areas during each El Niño or La Niño event; there is marked inter - El Niño and inter La Niña variation in late summer and annual rainfall; and that there has been a significant shift in the timings of maximum rainfall anomalies during El Niño episodes from an earlier investigation. The effects of rainfall on the wheat yield vary spatially, but are most apparent in the Free State where severe droughts have resulted in reduced yields. In the Northern Cape and Western Cape anomalously wet conditions, especially in late summer, coincide with reduced wheat yields. The ENSO - wheat yield relationship is not a simple linear one, and despite yields in the Northern Cape and Western Cape tracking Pacific sea surface temperatures by nearly a year, El Niño and La Niña years are not synonymous With increased or decreased yields in any province. ln fact, maximum and minimum yields in the Free State and Northern Cape are found in the year of, or year following a La Niño event, and consequently the present predictability of wheat yields by ENSO is limited. The relationships between ENSO, rainfall and wheat yield in South Africa is not readily apparent, which may be due to the short (<30 years) data set or mediating factors outside this study such as farm - management strategies or hemispheric variation in the evolution of El Niño and La Niña events.

Includes bibliographical references.
Wheat producers in the South Western Cape (SWC) of South Africa need to cope with biophysical and socio-economic systems exposing farmers to a multidimensional decision- making environment. The rain fed wheat production in the Swartland region is highly susceptible to the interannual variability of winter rainfall. Producers, therefore, need relevant climatic information to identify ways to improve profitability and to make sound economic decisions. Seasonal forecasting has the potential to provide wheat producers with invaluable information regarding the climatic conditions. However, due to the complex nature of the atmospheric dynamics associated with winter rainfall in South Africa, seasonal forecasting models have been found to have very little skill in predicting the variability of winter rainfall. Such a shortfall has created a gap for which this study has attempted to bridge. This study aimed to investigate the relationship between wheat-specific rainfall characteristics, large-scale modes of climate variability and wheat yields in the Swartland region to assess whether these relationships could provide useful climatic information to the wheat farmers. Six wheat-specific rainfall characteristics (total rainfall ; number of wet days ; number of ‘good’ rainfall events; number of heavy rainfall events; percentage ‘good’ rainfall ; and the number of dry dekads ) on various time scales (winter; seasonal; monthly and dekadal) were correlated against wheat yield records over a 17 year period from 1994 to 2010. From this analysis, the distribution and timing of the rainfall throughout the wheat growing season (April to September) emerged as an important determinant of wheat yield. An accurate statistical wheat prediction model was created using farmer stipulated rainfall- wheat yield thresholds. Three teleconnections (El Niño-Southern Oscillation [ENSO], Antarctic Oscillation [AAO] and South Atlantic sea surface temperatures [SSTs]) represented by eight climate indices (Nino 3.4 Index, Ocean Nino Index [ONI], Southern Oscillation Index [SOI], AAO index, Southern Annular Mode Index [SAM], South Atlantic Dipole Index [SADI], South Western Atlantic SST Index [SWAI] and South Central Atlantic SST Index [SCAI]), were correlated against wheat yield data over a 17 year period from 1994 to 2010. The relationships between the three teleconnections and wheat yield in the Swartland were established. Teleconnection-wheat yield correlations were found to be limited, with regards to the application of this information to farmers, due to the lack of a comprehensive understanding of the dynamics of how the three teleconnections influence the local climate and, therefore, the wheat yield in the Swartland. The eight climate indices, representing the three teleconnections, were correlated against the six wheat-specific rainfall characteristic indices from each of the three study areas over the period from 1980 to 2012. The state of ENSO during the first half of the year was shown to be correlated with rainfall characteristics during both the first (April to July) and second (July to September) halves of the wheat growing season; however, these correlations differ ed in their sign. Correlations suggested a negative phase of AAO was associated with above normal rainfall throughout the year across the Swartland region. Sea surface temperatures in the central South Atlantic during March to October showed significant negative correlations with rainfall during the latter half of the wheat growing season (July to October) across the Swartland region. This study presented evidence supporting the plausibility and validity for the use of the state of large-scale modes of variability in the prediction of wheat-specific rainfall characteristics and aggregated yields in the Swartland region. This has the potential to provide useful information to wheat farmers in the Swartland to aid in their decision making process

On montre que la resistance du ble a la contrainte hydrique est associee au maintien d'un nombre d'epis fertiles et d'un nombre de grains par epi eleves, a une petite taille du grain et a une capacite de recuperation elevee. On a evalue les besoins globaus optima en eau a 440 mm et on a montre qu'une mauvaise efficacite de l'utilisation de l'eau peut etre la consequence d'un developpement foliaire surdimensionne. Une production en grains stable en cas de carence hydrique est liee a une photosynthese globale elevee, a de grandes capacites d'accumulation et de mobilisation der reserves glucidiques. Les mecanismes de resistance differant d'une variete a l'autre, on tente de definir un ideotype de ble adapte aux zones arides

Dans les pays du Sud ruraux et à faibles revenus, la vulnérabilité des zones agricoles pluviales, face à la variabilité pluviométrique, nécessite de trouver des solutions efficaces pour limiter les effets des aléas climatiques sur les récoltes. La prévision des caractéristiques des saisons des pluies quelque temps avant leur démarrage devrait aider à l’établissement de stratégies agricoles d’adaptation aux aléas pluviométriques. C’est à cet objectif que s’attache ce travail, appliqué à l’Afrique de l’Est (Kenya et nord de la Tanzanie), et articulé en 3 parties :- Définir et comprendre le comportement des descripteurs intra saisonniers (DIS) qui feront l’objet de l’étude de prévisibilité. Un travail spécifique a permis le développement d’une nouvelle approche méthodologique dans la manière de définir les démarrages (DSP) et fins (FSP) de saisons des pluies à l’échelle régionale. Cette approche basée sur une analyse multivariée, permet de s’affranchir des choix subjectifs de seuils pluviométriques imposés par les définitions communément utilisée en agro-climatologie. Une analyse de cohérence spatiale à l’échelle inter annuelle montre que, pour les deux saisons des pluies (long rains et short rains), le cumul saisonnier et le nombre de jours de pluie présentent une forte cohérence spatiale, tandis qu’elle est plus modérée pour le démarrage et fin des saisons et faible pour l’intensité quotidienne moyenne.- Analyser la prévisibilité des DIS aux 2 échelles spatiales régionale et locale en s’appuyant sur les simulations numériques du modèle climatique global ECHAM 4.5. Les précipitations quotidiennes simulées par le modèle, même après correction des biais, ne permettent pas d’appréhender correctement la variabilité interannuelle des DIS. Une spécification de la variabilité des DSP et FSP menée par le biais de modèles statistiques construits à partir d’indices climatiques observés, présuppose une prévisibilité modérée des deux descripteurs à l’échelle locale (régionale), et cela quelle que soit la saison. Le développement de modèles statistico-dynamiques à partir des champs de vents simulés par ECHAM 4.5, en mode forcé par les températures marines observées d’une part et prévues d’autre part, montre également des performances faibles localement et régionalement. - Explorer la manière dont la variabilité spatio-temporelle des paramètres climatiques et environnementaux module la variabilité des rendements de sorgho. Ces rendements sont simulés par le modèle agronomique SARRA-H à partir de données climatiques observées (1973-2001) dans 3 stations localisées à différentes altitudes le long des pentes orientales du Mt Kenya. Le cumul précipité et la durée de la saison expliquent une part importante de la variabilité des rendements. D’autres variables apparaissent comme jouant un rôle non négligeable ; le nombre de jours de pluies, l’intensité quotidienne moyenne ou encore certains DIS relatifs à l’organisation temporelle des pluies au sein d’une saison en font partie. L’influence des autres variables météorologiques est seulement visible pour les ‘long rains’ avec une covariation négative entre les rendements et les températures maximales ou, le rayonnement global. La date de semis semble jouer un rôle dans la modulation des rendements pour les stations de haute et moyenne altitudes, mais avec des différences notables entre les deux saisons des pluies
In Southern countries with rural low income populations, the vulnerability of rainfed agriculture to rainfall variability requires effective solutions to mitigate the effects of climatic hazards on crops. Predicting the characteristics of rainy seasons some time before they start should help the establishment of agricultural adaptation strategies to rainfall hazards. This is the objective of the present study, focused on East Africa (Kenya and northern Tanzania), and divided in three parts:- Define and document intra-seasonal descriptors (ISD) that will be considered in the predictability study. A new methodological approach has been developed in order to define the onset date (ORS) and the cessation date (CRS) of the rainy seasons at the regional level. Based on a multivariate analysis, it eliminates the subjective choice of rainfall thresholds imposed by the definitions commonly used in agroclimatology. An analysis of spatial coherence at interannual time-scale shows that for the two rainy seasons ("long rains" and "short rains"), the seasonal amount and the number of rainy days have a high spatial coherence, while it is medium for the onset and cessation dates and low for the average daily rainfall intensity.- Analyze the predictability of the ISD at both regional and local scales based on numerical simulations from the global climate model ECHAM 4.5. Daily precipitation simulated by the model, even after bias correction, do not correctly capture the IDS interannual variability. A specification of the ORS and CRS variability using statistical models applied to observed climate indices, suggests quite a low predictability of the descriptors at the local (regional) scale, regardless of the season. The development of statistical-dynamical models from wind fields simulated by ECHAM 4.5, in experiments forced by either observed or predicted sea temperatures, also shows quite poor skills locally and regionally.- Explore how the space-time variability of climatic and environmental factors modulate the variations of sorghum yields. Crop yields are simulated by the agronomic model SARRA-H using observed climate data (1973-2001) at three stations located at different elevations along the eastern slopes of Mt Kenya. The seasonal rainfall accumulation and the duration of the season account for a large part of the yields variability. Other rainfall variables also play a significant role, among which the number of rainy days, the average daily intensity and some ISD related to the temporal organization of rainfall within the season. The influence of other meteorological variables is only found during the long rains, in the form of a negative correlation between yields and both maximum temperature and global radiation. Sowing dates seem to play a role in modulating yields for high and medium altitude stations, but with notable differences between the two rainy seasons

Two field trials and a regional survey were conducted in Vitis vinifera L.Merlot vineyards located in California over several seasons to investigate the effects of weather variables such as rainfall and growing degree days and vineyard management practices, such as irrigation and fertilization, on the main compounds responsible for fruit and wine green aromas, 3- isobutyl -2 -methoxypyrazine (IBMP) and C 6 compounds. In the first study, the concentration of IBMP and C6 compounds in fruit harvested from 69 commercial vineyards located in three distinctly different wine grape growing regions were measured at commercial maturity from 2007 to 2010. Seasonal variation of green aromas was found to be more important than regional variation, with similar trends among regions observed between for each season. The temperature during the spring, i.e. a period of active vine growth, was found to be the main driver of fruit green aromas at harvest, likely due to interactions with vine vigour and fruit shading. A first field trial was conducted in 2009 and 2010 to investigate the influence of irrigation and N fertilization on green aromas in fruit and wine. Experimental treatments comprised two irrigation levels (the standard irrigation rate of 70% ETc, and 100% of ETc) and a higher than standard nitrogen fertilisation (60 kg/ha, also at 100% of ETc). Irrigation and nitrogen fertilization promoted canopy growth and the decreased fruit exposure resulted in elevated levels of IBMP through fruit maturation compared to the standard irrigation. However, C6 compounds were not affected by either factor. Fruit colour and aroma precursors were higher under deficit irrigation conditions, while vine yield decreased significantly. Wines made with fruit derived from the deficit irrigation treatment were perceived as having less intense vegetal notes, and enhanced fruit characters compared to those from the non deficit treatment. The additional application of nitrogen fertilizer also had a significant and positive effect on the vegetal perception of wines. A second field trial involving exclusion of winter rainfall was also conducted during the 2009 and 2010 growing seasons. Control vines were exposed to normal rainfall conditions, while winter rainfall was excluded from experimental vines by covering the ground with a plastic tarpaulin during the entire dormant season. During the growing season, irrigation in both treatments was maintained at a rate of 70%; of crop evapotranspiration (ETc) until commercial harvest. Canopy growth, berry size and vine yield were significantly reduced on the vines from the rainfall exclusion treatment, and a significant increase in the fruit to pruning weight ratio was recorded over time. IBMP concentration was greater under normal rainfall conditions, and fruit levels remained significantly higher during the season compared to fruit from vines that did not receive winter rainfall. Significantly different concentrations of C6 compounds were only observed in rainfall exclusion fruit towards the end of the second season. Fruit and wine quality parameters, mainly colour and mouth feel compounds, were positively affected by the absence of rainfall in both years. Descriptive analysis indicated that wines from the rainfall exclusion treatment were perceived as being less green and more fruity in the first season. However, as a consequence of the reduction in vine growth, the same treatment produced less fruity wines, of inferior tannin quality in the subsequent season. These findings demonstrate for the first time that vineyard management practices affect fruit and wine IBMP levels, but have no significant impact on the concentration of C6 compounds. As such, grape growers seeking to minimise IBMP fruit levels at harvest would benefit from reduced water and nitrogen application in the vineyard. Furthermore, these results show the importance of achieving adequate canopy growth early in the season, especially under low or no rainfall conditions. Otherwise, the positive effects on fruit and wine quality achieved through reduced berry size may be offset by an even more significant reduction in total yield and a severe lack of balance between vegetative and reproductive growth.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2012

Agricultural production is highly sensitive to climate and weather perturbations. Maize is the main crop cultivated in South Africa and production is predominantly rain-fed. South Africa’s climate, especially rainfall, is extremely variable which influences the water available for agriculture and makes rain-fed cropping very risky. In the aim to reduce the uncertainty in the climate of the forthcoming season, this study investigates whether seasonal climate forecasts can be used to predict maize yields for South Africa with a usable level of skill. Maize yield, under rain-fed conditions, is simulated for each of the magisterial districts in the primary maize producing region of South Africa for the period from 1979 to 1999. The ability of the CERES-Maize model to simulate South African maize yields is established by forcing the CERES-Maize model with observed weather data. The simulated maize yields obtained by forcing the CERES-Maize model with observed weather data set the target skill level for the simulation systems that incorporate Global Circulation Models (GCMs). Two GCMs produced the simulated fields for this study, they are the Conformal Cubic Atmospheric Model (CCAM) and the ECHAM4.5 model. CCAM ran a 5 and ECHAM4.5 a 6- member ensemble of simulations on horizontal grids of 2.1° x 2.1° and 2.8° x 2.8° respectively. Both models were forced with observed sea-surface temperatures for the period 1979 to 2003. The CERES-Maize model is forced with each ensemble member of the CCAM-simulated fields and with each ensemble member of the ECHAM4.5-simulated fields. The CERES-CCAM simulated maize yields and CERES-ECHAM4.5 simulated maize yields are combined to form a Multi-Model maize yield ensemble system. The simulated yields are verified against actual maize yields. The CERES-Maize model shows significant skill in simulating South Africa maize yields. CERES-Maize model simulations using the CCAM-simulated fields produced skill levels comparable to the target skill, while the CERES-ECHAM4.5 simulation system illustrated poor skill. The Multi-Model system presented here could therefore not outscore the skill of the best single-model simulation system (CERES-CCAM). Notwithstanding, the CERES-Maize model has the potential to be used in an operational environment to predict South African maize yields, provided that the GCM forecast fields used to force the model are adequately skilful. Such a yield prediction system does not currently exist in South Africa.
Dissertation (MSc)--University of Pretoria, 2009.
Geography, Geoinformatics and Meteorology
Unrestricted

碩士
國立中興大學
水土保持學系所
107
How to estimate sediment yield of slopeland is an important working item in watershed planning. The characteristics of rainfall, land cover and soil texture in the watershed affect the surface runoff, soil loss and sediment yield. Generally, the sediment yield is verified by the suspension load derived from the hydrologic station. However, the hydrologic station in the upstream is difficult to set up and manage due to the topographical condition, which results in the lack of observed information. This study established a concept model using the environmental indicators to estimate the spatial distribution of excess rainfall and sediment yield in the watershed. Chenyoulan watershed was selected as a sample area. Risk assessment concepts coupled with environmental indicators are used to establish models, which take excess rainfall index as hazard, topographic wetness index as vulnerability and sediment delivery ratio as exposure indicator, for calculating the quantitative relationship among rainfall, runoff and sediment yield. Discharge and suspension load recorded at Neimaopu hydrologic station over the years were used to calculate the sediment yield of each storm event. Finally, the relationship (Qc =0.9593Q-4E+07, R²=0.7383, p ＜0.01, and Sc =496781e^3.5696s, R²=0.75, p ＜0.01) between measured and observed runoff and sediment yield was estimated by regression analysis respectively. Total sediment yield caused by the event was distributed to each grid according to the weight of sediment yield potential. Finally, screen the hotspots of high sediment yield potential through the slope-unit with 50 hectares threshold of river network can be the reference of sediment management in the watershed.

Abstract After deregulation of the agricultural markets in South Africa in 1997, the estimated maize crop could no longer be verified against the actual crop, due to the lack of control data from the Maize Control Board. This drove the need to explore remotely sensed data as a supplement to the current crop estimation methodology to improve crop estimations. Input data for the development of a Geographic Information System (GIS)-based model consisted of objective yield point data, Moderate Resolution Imaging Spectroradiometer (MODIS) Normalised Difference Vegetation Index (NDVI) images and rainfall grids. Rainfall grids were interpolated from weather station data. NDVI values were obtained from the MODIS sensor aboard the Terra platform. Objective yield point field survey data for the 2001/2002 growing season were utilised since dry-land or irrigated conditions were recorded for that season. MODIS NDVI values corresponded well with the growing stages and age of the maize plants after being adjusted to reflect the crop’s age rather than the Julian date. Rainfall values were extracted from rainfall grids and also aligned with the age of the maize plants. This is a suggested alternative to the traditional method of using the mean NDVI for several districts in a region over a Julian growing period of 11 months according to Julian dates. South African maize production areas extend over seven (7) provinces with eight (8) different temperature and rainfall zones (du Plessis, 2004). Planting-date zones based on the uniform age of the maize plants were developed from objective yield Global Positioning System (GPS) points for the 2001/2002 growing season and compared with the 2004/2005 growing season (Frost and Kneen, 2006). Planting dates were interpolated from these planting zones for objective yield GPS points which were missing planting dates in the survey database. MODIS imagery is affordable (free) and four (4) images cover the whole of South Africa daily, while one (1) image covers the study area daily. Several recommendations, such as establishing yield equations for a normal, dry, and wet season were made. It is also suggested that dry-land and irrigated areas continue to be evaluated separately in future.

Wheat (Triticum aestivum) production is important to global food security and the livelihoods of those who cultivate it. Increases in water-limited potential yield (PYw) and farm yield (FY) are necessary to keep pace with global demand, and in order for Australian growers to remain competitive in a changing climate and with declining terms of trade. In drought prone environments such as south-eastern Australia, alignment of the key developmental stage of flowering to the period that is optimal for the local climate is a critical determinant of yield. The optimal flowering period (OFP) begins when the risk of frost decreases, and ends to avoid increasing temperature, heat and water stress during grain fill. Flowering time is a function of the interaction between the speed of plant development (genetic, G), establishment date (management, M) and prevailing seasonal conditions (environment, E). Autumn rainfall decline, extreme spring weather and increasing farm size challenge traditional G x M combinations which are currently used to achieve the OFP in south-eastern Australia i.e. predominately fast developing spring wheats sown in late-April to early May. The objective of this study was to identify novel G x M combinations that stabilise flowering and maximise yield under changing rainfall patterns and recent changes to farming systems. This study used crop simulation and conducted field experiments in Temora, New South Wales (NSW); Berriwillock, Victoria; Minnipa, South Australia and Cunderdin, Western Australia. Firstly, OFPs were quantified in south-eastern Australia, the area most affected by autumn rainfall decline to align novel G x M strategies accordingly. Simulation demonstrated that the predicted timing and duration of OFPs varied with site and season. The relative importance of seasonal water supply and demand and extremes of temperature in defining the window also varied. To identify the physiological changes associated with breeding, the PYw and other parameters were quantified and compared at common sowing or flowering dates with a historic set of NSW cultivars released between 1901 and 2014. Genetic improvement through this period, increased grain yield at a rate of 26 kg ha-1 pa-1 regardless of sowing or flowering dates. The slow development and stable flowering observed in historic cultivars and superior partitioning to grain of modern cultivars were independent, and could potentially be combined in new cultivars to achieve future yield gains. Yield results for a novel fast-winter genotype (FW, with photoperiod insensitivity and requiring vernalisation) grown in a diverse set of environments, supported this hypothesis. The FW development pattern extended sowing windows while achieving 10-20% higher yields than current spring cultivars. The flowering stability index (1 minus the ratio of range in thermal time for flowering for each cultivar, to the range in thermal time of sowing dates) of the FW genotype was improved for the sowing dates currently used by farmers. Finally, novel agronomic packages to capture the higher yield potential of FW cultivars was investigated using simulation. Reliance on irregular rainfall to establish FW wheat could be reduced, and early establishment opportunities increased by sowing genotypes with long coleoptiles into stored sub-soil moisture accumulated during fallow. Combining the G x M flowering date stabilising factors; winter wheat, long coleoptile, early sowing and fallow reduced the reliance on autumn rainfall for timely crop establishment to provide a further buffer against seasonal climate variability. Consequently, simulated whole farm yield was increased as a greater area of wheat flowered during the optimal period. To achieve the productivity increases demonstrated here requires continued collaboration between agronomists and breeders. This includes the development of winter wheat cultivars with long coleoptiles that are adapted to different growing season lengths and OFPs, such that crops can be established earlier and emerge from a greater depth than current cultivars.

Tillage, stubble retention and nitrogen fertilization are management practices that influence the productivity and sustainability of rainfed cropping systems. However, the application of these practices is limited by our understanding of the mechanisms that contribute to crop growth and yield, including water and nitrogen use efficiency. Canopy development and patterns of leaf senescence alter the partitioning of water and nitrogen (N) use, both before and after flowering, which impacts grain yield. The two central questions for this research were: (1) what are mechanisms of canopy development that contribute to yield in no-till and stubble retention systems?; and (2) under what circumstances do they increase yield, water and N use efficiency? The aims for this thesis were to evaluate crop response to no-till, stubble retention and N fertilization, in the contrasting systems of wheat (Triticum aestivum L.) and maize (Zea mays L.), to better understand mechanisms that regulate crop growth, patterns of senescence and yield, in addition to water and nitrogen use efficiency (NUE). A physiological approach that linked the traits regulating crop growth and yield was used to interpret crop responses to treatments. It is hypothesised that there are similarities in the mechanisms operating in no-till and stubble retention systems that could be improved to increase yield. Field experiments were conducted in the dryland wheat growing environments of southern Australia and in maize systems in a sub-humid tropical environment in Kenya. In Australia, experiments were conducted at Roseworthy and Karoonda using two tillage treatments (conventional tillage, CT and no-till, NT), four rates of stubble (zero, low, moderate and high) and three N timings, splitting the application of 100 kg N ha⁻¹ between sowing, tillering (GS22) and awn emergence (GS49) in the ratios of 100-0-0, 25-50-25, 0-50-50. At Roseworthy, historic Australian wheat varieties were evaluated under NT with the retention of moderate amounts of stubble and under CT without stubble. In Kenya, field experiments were conducted at Embu research station to evaluate the responses of maize to CT and NT, three amounts of stubble (0, 3 and 5 t ha⁻¹) and N rates of 0, 80 and 120 kg N ha⁻¹, as well as timing the of supply of 80 kg N ha⁻¹ at sowing, six leaf stage (V6) and 12-leaf stage (V12) in the fractions of 0-0-0, 80-0-0, 27-53-0, 27-27-27 and 0-40-40. Wheat grain yield ranged from 1.5-3.2 t ha⁻¹, and the effects of tillage were marginal. Grain yield increased from bare ground up to the application of moderate amounts of stubble but reduced at high amounts of stubble. Benefits of water capture and storage did not improve with the application of high amounts of stubble. Crop growth rate (CGR) between stem elongation and flowering was inversely correlated with tiller numbers, and explained most of the treatment differences. Sowing application of N produced large vegetative biomass which led to a decrease in CGR and radiation use efficiency between stem elongation and flowering, resulting in a decrease in grain yield compared with delayed N supply. Five decades of selection has not provided greater adaptation to NT and stubble retention in Australian wheat, despite grain yield increases of 21 kg ha⁻¹ year⁻¹ between 1958 and 2011. Substantial changes in canopy architecture were detected from older taller varieties with closed canopies to modern short-stature varieties with more open canopies. Modern varieties had greener leaves but showed faster rates of leaf senescence compared with the older counterparts. Maize grain yield ranged from 2.3-5.3 t ha⁻¹, with small effects from tillage and stubble supply. Rate and timing of N supply produced large effects and modified crop response to tillage and stubble. When stubble was removed, grain yield reduced by 10% while water storage at sowing decreased by 8% under NT compared with CT. Crop growth rate between six-leaf stage (V6) and flowering, and nitrogen nutrition index (NNI) partially explained treatment differences. Retention of stubble reduced CGR and NNI compared with bare ground. The value of stubble in water storage at sowing, and crop growth and yield was greater in a season that received < 300 mm rainfall compared with where rainfall was > 600 mm. Delaying N supply increased NNI, CGR and traits associated with NUE and grain yield compared with sowing applications of N. Patterns of senescence in maize, at both whole-plant and canopy-layer scales were marginally impacted by tillage and stubble retention. Leaf senescence was primarily driven by N supply and sink size. Time to loss of 50% of maximum leaf greenness was earlier in fertilized crops but delayed in the unfertilized controls. Rate of senescence was faster in fertilized crops compared with unfertilized controls at both whole-plant and canopy-layer scales. Grain yield, kernel number and nitrogen remobilization efficiency were associated with a faster rate of senescence in the top and mid layer leaves but with slower rates of senescence in the bottom layer. There were similarities in treatment effects and the mechanisms that regulated crop growth and yield between the two systems: (1) Grain yield was a function grain number, which in turn was proportional to CGR during the critical period of determination. Strategic supply of N at sowing and later stages increased CGR during the critical period for grain set, improved NNI and increased RUE, hence higher grain yield; (2) Grain yield was maximized at 2-3 t ha⁻¹ of stubble as demonstrated by the analysis of yield gaps, potentially due to water capture and storage and the regulation of soil temperature which impacted emergence and early growth; (3) N supply and sink size modified the patterns of senescence in both crops, whereby faster rates of senescence were associated with higher grain yield; and (4) N supply modified crop response to tillage and stubble. Treatment interactions were few, and varied with N supply and season. Effects of tillage system were marginal and independent of season. A mechanistic approach is discussed, which links treatment effects and the mechanisms regulating grain yield. In conclusion, the mechanisms of canopy development and yield limitation operating in NT and stubble retention were similar in both cropping systems. Higher fertilizer N rates and better timing of N supply are required for yield improvement in NT and stubble retention systems. While NT alone reduced yield, moderate amounts of stubble can improve water storage and grain yield, but this is subject to seasonal rainfall. Critical thresholds of 2-3 t ha⁻¹ of stubble indicate amounts over this limit could be allocated to alternative uses. Results show the importance of interpreting crop responses to NT and stubble retention on the basis of physiological principles.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Agriculture, Food and Wine, 2018

碩士
國立屏東科技大學
水土保持系所
99
The average annual rainfall in Taiwan is 2510 mm, and it is 2.6 times the world average. With 78% of the rainfall concentrated in the rainy season, most rainfall from the extreme rainfall of typhoon, and the growing problem of global climate change in recent years, the concentrated rainfall in Taiwan is a significant feature. The 2009 Typhoon Morakot, for instance, was found to rewrite the history of maximum rainfall again. The huge precipitation would result in critical debris avalanche and seriously endanger downriver people's lives and property. Hence, the current research was aimed to probe into the increased volume of collapse after raining for the precipitation area by utilizing the data of extreme rainfall to deduce the appropriate Daogi formula to further figure out a reasonable equation to estimate the average depth of the collapse. The results exhibited that the definition of 1% to the average of extreme rainfall for the Daogi formula, with the average error rate of 5%, would obtain more accurate estimation than others. It was also found that the average depth of the landslide by use of the gradient depth calculation would represent the overall average depth of the landslide. The value 8.3m was discordant in contrast with the previous study by the depth of 3.3m difference. This phenomenon might be due to the high rainfall. Moreover, the findings revealed that the increased volume of collapse sediment yield deduced from Daogi formula, which was derived from the increased volume of collapse area multiplied by the average depth of collapse, was underestimated. This underestimation could be ascribed to the neglect of the capacity of sediment yield in the original collapse area.

University of Technology Sydney. Faculty of Science.
Wheat is the most important crop in Australia in terms of the gross value of production. However, in Australia wheat yield is extremely variable from year to year among major production regions, such as New South Wales (NSW), with its agricultural system being significantly affected by water stress and ongoing climate change. To accurately quantify crop yield, and estimate greenhouse gas emissions (GHG) at specific sites and regional scales, it is essential to link spatial information of agro-resources and crop simulation model to assess crop growth in response to agricultural management and environmental variation. The outcomes of this project will enhance the capability of farmers and policy makers to adapt and manage farm outcomes in the face of climate change/variability. For this study, I extracted the historical daily climate data (1900-2010), known as SILO patched point dataset (PPD, http://www.longpaddock.qld.gov.au/silo/ppd/index.php), for maximum and minimum temperature, rainfall, and solar radiation at 894 weather stations evenly distributed across the NSW wheat belt. Wheat yields at shire level during 1922-2000 (data in some shires were not available in some years) across the NSW wheat belt were obtained from Fitzsimmons (2001). Statistical methods were used to quantify the relationship between reported shire wheat yields and climate factors during the wheat-growing season across the NSW wheat belt in eastern Australia from 1922 to 2000. I found that wheat yields were positively correlated to rainfall and minimum temperature while negatively correlated to maximum temperature at a significant level (p<0.05). Growing season rainfall is usually the main direct climatic driver affecting wheat yields variation in this semi-arid area, but the indirect effects of temperature and solar radiation are also important. A detailed understanding of how historical climate variation has impacted on wheat yield can provide useful insights for the development of sustainable agricultural systems in the face of future climate change. I used the statistical downscaling and bias-correction method developed by Liu and Zuo (2012) to generate realistic daily site-specific climate data from monthly GCM output on a coarse-resolution grid. Briefly, monthly GCM output data (solar radiation, rainfall, daily maximum and minimum temperature) from each of the selected GCMs were downscaled to the 894 observation sites using an inverse distance-weighted interpolation method. Biases were then corrected using a transfer function derived from interpolated GCM data and observed data for the sites. Daily climate data for each of 894 sites under two RCPs for 1900-2100 were generated by a modified stochastic weather generator (WGEN) with parameters derived from the bias-corrected monthly data. The results show that wheat growing season rainfall is projected to decrease under different future scenarios across the NSW wheat belt. Future climate projected an averaged warming of 2.1˚C for RCP4.5 and 3.8˚C for RCP8.5 across this region in 2061-2100 compared to the baseline period 1961-2000. A crop simulation model (APSIM) driven by statistical downscaling data was used to simulate wheat productivity and water use efficiency under the CMIP5 multimodel ensemble projections across the NSW wheat belt. Despite an acceleration of crop development and shortening of growth duration together with declining growing season rainfall, GCMs projected that multi-model median yields could increase by 0.4% (4704 kg/ha) for RCP4.5 and 7.3% (5027 kg/ha) for RCP8.5 by 2061-2100. These results show that drier area would benefit more from elevated CO₂ than wetter area in the NSW wheat belt. Without the increase in CO₂ concentration simulated wheat yield decrease rapidly under RCP4.5 by 2061-2100 and much more so under RCP8.5 compared to the present. The simulated evapotranspiration (ET) decreased by 11.9% (282 mm) for RCP4.5 and 18.8% (260 mm) for RCP8.5 over the whole wheat belt. Increasing yields combined with decreasing ET resulted in simulated water use efficiency increasing by 11.4% (15.4 kg ha⁻¹ mm⁻¹) for RCP4.5 and 29.3% (17.8 kg ha⁻¹ mm⁻¹) for RCP8.5. Wheat production in water-limited, low yielding environments appears to be less negative impacted or in some cases even positively affected under future climate change and elevated CO₂, compared to other growing environments in the world. Agro-ecosystems have high spatial heterogeneity and temporal variation of productivity, arising from the spatial and temporal variability of climate, soil texture/water, and management practices. Furthermore, the projected yield increase in the future could be overestimated because the crop model generally does not sufficiently account for yield reduction due to diseases, pests and weeds. I did not explicitly consider certain aspects such as efficient management practices, breeding new crop cultivars, which will obviously have a significant impact on wheat yield in the future. Therefore, these current simulated results would provide a baseline for future adaptive strategies such as incorporating new traits into new cultivars in new management systems not currently available.

Winter wheat is commonly grown in dryland cropping systems in the Pacific Northwest region of semi-arid eastern Oregon. For agronomic, economic, and environmental reasons, it is important to understand the long-term sustainability of such dryland systems. The objective of this study was to evaluate the long-term effects of tillage, nitrogen (N), soil depth, and the influence of precipitation on wheat yields in dry land cropping systems of eastern Oregon. Data were taken from the Tillage/Fertility or "Balenger" experiment, which was established in 1940 by a Soil Conservation employee, and is one of the oldest replicated research experiments in the western United States. The experiment consisted of a winter wheat-summer fallow rotation arranged in a randomized block design with three replications. The main plot consisted of three primary tillage treatments (moldboard plow, offset disk, and subsurface sweep) and subplots consisted of six nitrogen treatments that changed over time and most recently ranged from 0 to 180 kg ha�����. Soil depth of individual plots ranged from 1.2- to 3.0-m. The study was divided into four main time periods (1940-1951, 1952-1961, 1962-1987, and 1988-1997) within which experimental treatments were consistently maintained. The moldboard plow tillage treatment significantly increased yields by more than 300 kg ha����� over the subsurface sweep tillage treatment in all four time periods. Yields with the moldboard plow system were significantly higher than with the offset disk system in time periods 3 and 4. The same trend was evident for mean yield in time periods 1 and 2, but differences were not statistically significant. In time periods 1, 2, and 3, mean yields were higher with the offset disk tillage treatment than the subsurface sweep tillage system, although the differences were not statistically significant. In time period 4, mean yield was higher for the subsurface sweep system than the offset disk treatment, but differences were not statistically significantly. The optimum amount of N for winter wheat differed from year to year, within, and between experiment periods. This was apparently in response to rainfall patterns and improved management factors, specifically more N responsive semi-dwarf varieties. For time period 1, the maximum fertilizer rate was 11.2 kg N ha�����, which tended to produce higher mean grain yields than an application rate of than 0 kg N ha�����, regardless of the quantity or distribution of precipitation. For time period 2, the maximum fertilizer rate was 33.7 kg N ha�����, which produced significantly higher grain yields than an application rate of than 0 kg N ha�����, regardless of the quantity or distribution of precipitation. For time period 3 (1962-1987), which had below-normal annual and growing season precipitation, yield increased with the addition of 45 kg N ha�����. For time period 4 (1988- 1997), which had above-normal annual and growing season precipitation, yield increased with the addition of 90 kg N ha�����. Yield increases at greater rates of N were insignificant. For time periods 3 and 4, maximum mean yield was obtained at an application rate of 135 kg N ha�����. The response of wheat yield to N during dry years was greater for deep (> 2.8 m) soils than for shallow soils. In addition to amount, rainfall distribution during the winter (October to March) and growing (April to June) season significantly affected yield. Results demonstrate the importance of rainfall and nitrogen to winter wheat production in eastern Oregon, and that the most environmentally sound tillage systems are not necessarily the most profitable from farmers' point of view.
Graduation date: 2000

M.Sc. (Geography)
The 1982/1983 drought in the summer rainfall regions of South Africa highlighted the dependence of the agricultural sector as well as the general economy of the country on climatic vagaries. The results as indicated in this dissertation fonn a basis for the development of a yield prediction model for maize in the south-eastern Transvaal. The study consists of two parts, namely:- a) The delimitation of the south-eastern Transvaal into smaller homogeneous rainfall regions. b) An investigation of spatial and temporal rainfall patterns within each region and over the study area as a whole. a) The delimitation of the south-eastern Transvaal into smaller homogeneous rainfall regions: Various methods were investigated for this purpose and T-mode Principal Components Analysis with the subsequent clustering of component scores were found to be the most acceptable. b) An investigation of spatial and temporal rainfall patterns within each region and over the study area as a whole: Various parameters such as rainfall amount~ number of rain-days~ rainfall intensity~ seasonality and variability of rainfall were analysed. The presence of rainfall cycles and absence of linear trends were established. The orographic effect of the Eastern Escarpment on the spatial distribution of rainfall amount, frequency and intensity is clearly shown. Areas where conditions are less suitable for the dry-land cultivation of crops due to factors such as rainfall variability (in excess of 30%), steep slopes and relatively low rainfall intensity, were identified. Significant correlations were found between spring and late summer rainfall of a dry year

碩士
國立中興大學
水土保持學系
93
This study estimated sediment yield in upstream watershed of Nan-Ao-Bei Creek and a tributary of Lainyang River. Using DEM（Digital Elevation Model）, SPOT images and GIS（Geographic Information Systems) technology to predict sediment transport mechanisms. In this study, the USLE (Universal Soil Loss Equation ) was used to estimate soil loss from slope lands. The method suggested by Khazai and Sitar was employed to predict the landslide quantity. Combining SDR (Sediment Delivery Ratio ), channel attenuation rate and precipitation, the watershed sediment yields can be estimated in a storm event. In the meantime, simulate hydrograph derived from GRAPH（Grid Rational Algorithm for Predicting Hydrograph）. Then discuss relationship of the simulation results and sediment yields. The results indicated that in upstream watershed of Nan-Ao-Bei Creek the sediment yield from slope land is 147,045.25 m3 per year, and average erosion depth is 0.4 cm per year. The landslide quantity is 2,317,090 m3 and average denudation depth is 1.55 m. The sediment yield（SY） equation about accumulate precipitation before peak discharge（r） for the upstream watershed of Nan-Ao-Bei Creek is SY＝66.593r+4838.7，R2＝0.9563*** .In the other watershed, the sediment yield from slope land is 13,746.71 m3 per year, and average erosion depth is 0.13 cm per year. The landslide quantity is 502,560 m3 and average denudation depth is 1.55 m. The sediment yield equation is SY＝6.4941r+649.57，R2＝0.9286**.