Dissertations / Theses on the topic 'Dryland'

Dryland Australia has a distinctive mammal fauna that has been severely impacted by novel threats since European colonisation. I aimed to understand the defining characteristics of mammal refuges in this region. In chapter 2 I used atlas data to compare the historic and contemporary distributions of dryland marsupials. The greater bilby and common brushtail possum have substantially contracted in distribution. The bilby was more likely to occur on land without cattle grazing and with low rabbit densities, while the possum has contracted to cooler areas. In chapter 3 I focused on the MacDonnell Ranges to understand the factors protecting declining mammals. Predation was supported as a major driver of extant mammal richness and vast areas of rugged terrain provide vital refuge for dryland mammals. In chapter 4 I consider the hypothesis that trophic competition between the dingo and cat creates refuge from predation for small mammals by analysing the diets of the two predators for evidence of competition. I conclude that habitat complexity underpins the refuge and that effects of dingo predation on the cat population are of secondary importance. In chapters 5-7 I focused on the critically endangered central rock-rat (CRR). My habitat suitability maps confirmed a dramatic range contraction for this species over the last 100 years and their current association with extreme ruggedness supported the hypothesis that the impact of cat predation is mediated by habitat complexity. I established the effectiveness of camera trapping for sampling the CRR and, using this sampling tool, found that CRR occupancy was positively associated with areas burnt within the past 5 years and that cats forage less frequently in areas with dense hummock grass cover. Fire management could be used as a tool for rodent conservation in this environment. In chapter 8 I synthesise my findings and provide a framework for research on declining fauna.

Semi-arid environments are mainly characterized by scarce water resources and are usually subject to risks of water stress. In these regions, water supply for drinking and irrigation purposes depends strongly on storage in surface reservoirs and sediment deposition in these reservoirs affects adversely the water storage. In order to reproduce the complex behaviour of sediment deposition in reservoirs located in semi-arid environments and the effects of using sediment management techniques, a reservoir sedimentation model is developed and coupled within the WASA-SED model, which simulates rainfall-runoff processes and sediment transport at the hillslope and river network. The reservoir sedimentation model consists of two modelling approaches, which may be applied according to reservoir size and data availability. For reservoirs with information about their geometric features (reservoir topography, stage-area and stage-volume curves) and physical properties of sediment deposits, such as deposition thickness, grain size distribution of sediment deposits and sediment densities, a detailed modelling approach of reservoir sedimentation may be applied. For reservoirs without those characteristics, a simplified modelling approach is used. The detailed modelling approach of reservoir sedimentation enables the assessment of sediment deposition pattern in reservoirs and the evaluation of sediment release efficiency of sediment management techniques. It simulates sediment transport along the longitudinal profile of a reservoir. The reservoir is divided into cross sections to elaborate the sediment budget. The sediment transport component is calculated using a non-uniform sediment transport approach based on the concept of sediment carrying capacity. Four different sediment-transport equations can be selected for the simulations. The simplified modelling approach of reservoir sedimentation is suitable to simulate water and sediment transfer in dense reservoirs network. Nevertheless, it allows simulating neither sediment management techniques, nor spatial distribution of sedimentation. In this approach, the reservoirs are classified into small and strategic reservoirs according to their location and size. Strategic reservoirs are medium and large-sized reservoirs located on main rivers at the sub-basin’s outlet or reservoirs of particular interest. The small reservoirs are located at tributary streams and represented in the model in an aggregate manner by grouping them into size classes according to their storage capacity. A cascade routing scheme is used to describe the upstream-downstream position of the reservoir classes. The water and sediment balances of small reservoirs are computed for one hypothetical representative reservoir of mean characteristics. Sediment trapping efficiency and effluent grain size distribution are estimated using the overflow rate concept. Three model applications are carried out within this research, as follows: • The detailed modelling approach of reservoir sedimentation is applied to the 92.2 Mm³ Barasona Reservoir, located in the foothills of the Central Pyrenees (Aragon, Spain). A two-stage calibration was performed to account for changes on the sediment deposition pattern caused by sediment management. The reservoir sedimentation model is then validated for another simulation period which confirms that the processes related to reservoir sedimentation are well represented by the model. • An application is carried out to the 933-km² Benguê catchment, located in the semi-arid region of Northeast Brazil. The catchment is characterized by a dense reservoir network, covering almost 45% of the catchment area, with a significant lack of data. Water and sediment balances of those reservoirs are computed using the simplified modelling approach. Three spatial configurations describing the cascade routing scheme are tested. • The reservoir sedimentation model is applied again to the Barasona reservoir to evaluate the sediment release efficiency of sediment management strategies. Cost analysis is presented to help in the choice of the most promising sediment management technique for that situation. Thus, the model enables the assessment of technical features of the sediment management strategies. Overall, simulation results are characterized by large uncertainties, partly due to low data availability and also due to uncertainties of the model structure to adequately represent the processes related to reservoir sedimentation.
Semiaride Gebiete sind hauptsächlich durch geringe Wasserressourcen gekennzeichnet und unterliegen häufig dem Risiko der Wasserknappheit. In diesen Gebieten ist die Wasserbereitstellung für Bewässerung und Trinkwasserversorgung stark von der oberflächlichen Speicherung in Stauseen abhängig, deren Wasserverfügbarkeit nachteilig durch Sedimentablagerung beeinflusst wird. Zur Wiedergabe des komplexen Sedimentablagerungsverhaltens in Stauseen von semiariden Gebieten und die Auswirkungen von Sedimentmanagementmaßnahmen wird ein Sedimentationsmodell entwickelt und mit dem WASA-SED Modell gekoppelt, das für die Modellierung der Abflussbildung und des Sedimenttransportes in Einzugsgebieten geeignet ist. Das Sedimentationsmodell beinhaltet zwei Ansätze, die unter der Berücksichtigung verschiedener Stauseengrößenklassen und Datenverfügbarkeit eingesetzt werden können. Für die Stauseen mit verfügbaren Informationen über ihre geometrischen Eigenschaften (wie Stauseetopographie und Höhe-Fläche-Volumen-Beziehung) und weitere Kenngrößen wie Ablagerungsmächtigkeit, Korngrößenverteilung und Sedimentdichte, kann ein detaillierter Modellansatz für die Sedimentablagerung verwendet werden. Wo diese Informationen nicht verfügbar sind, wird auf einen vereinfachten Ansatz zurückgegriffen. Der detaillierte Modellansatz ermöglicht die Betrachtung von Ablagerungsmustern im Stausee und Einschätzungen über die Effektivität von Sedimentmanagementmaßnahmen hinsichtlich der Sedimententlastung. Dieser Ansatz beruht auf der Simulation des Sedimenttransportes entlang eines Stauseelängsprofils. Für die Berechnung des Sedimenttransfers wird der Stauseekörper in einer Folge von Querprofilen repräsentiert. Der Sedimenttransport wird dabei korngrößenspezifisch entsprechend der Transportkapazität berechnet. Dafür stehen vier verschiedenen Sedimenttransportgleichungen zur Verfügung. Der vereinfachte Modellansatz ist für die Simulation des Sedimenttransfers in Gebieten mit hoher Stauseedichte geeignet, jedoch können weder Sedimentmanagementmaßnahmen noch die räumliche Verteilung der Ablagerungen berücksichtigt werden. Dafür werden die Stauseen in Abhängigkeit von ihrer Größe und Position in kleine und strategische Stauseen unterteilt. Dabei sind strategische Stausseen solche mit mittlerem bis großem Volumen sowie einer Lage im Hauptgerinne oder solche mit sonstiger besonderer Bedeutung. Kleine Stauseen hingegen befinden sich an den Nebenflüssen und werden im Modell in aggregierter Form durch ihre Einteilung in Stauseegrößenklassen repräsentiert. Ein Kaskadenverfahren wird für den Wasser- und Sedimentlauf zwischen den Stauseeklassen verwendet. Dabei werden für jede Stauseeklasse der Wasser- sowie Sedimenthaushalt für einen hypothetischen repräsentativen Stausee mit mittleren Eigenschaften berechnet. Die Sedimentaufnahme und die Korngrößenverteilung des abgegebenen Sediments werden mit dem Überlaufanteil-Ansatz berechnet. In dieser Studie werden drei Modellanwendungen vorgestellt: • Für den 92,2 Mio.m³-großen Barasona-Stausee (Vorland der Zentralpyrenäen, Aragon, Spanien) wird die Modellierung der Sedimentablagerung mit dem detaillierten Modellansatz vorgenommen. Die Kalibrierung dafür wurde in zwei Schritten durchgeführt, um Änderungen im Stauseemanagement Rechnung zu tragen. Die ModellValidierung wird schließlich für eine andere Simulationsperiode vorgenommen. Dabei wird ersichtlich, dass die Prozesse der Sedimentablagerung gut durch das Modell wiedergegeben werden. • Das Modell wird auf das 933 km²-große Benguê-Einzugsgebiet, das sich im semiariden Nordosten Brasiliens befindet, angewendet. Dieses Einzugsgebiet ist durch eine hohe Dichte an kleinen Stauseen, charakterisiert, die fast 45% des Gebietes umfasst, wofür jedoch wenige Messdaten verfügbar sind. Deshalb werden der Wasser- und Sedimenttransport mit dem vereinfachten Modellansatz berechnet. Dabei werden drei Konfigurationen des Kaskadenverfahrens getestet. • Die Modellanwendung erfolgt erneut für den Barasona-Stausee bezüglich der Effektivität der Sedimentmanagementmaßnahmen. Eine Kostenanalyse ermöglicht die Auswahl geeigneter Maßnahmen für den Stausee. Dadurch wird eine Beurteilung der verschiedenen Sedimentmanagementstrategien ermöglicht. Im Allgemeinen unterliegen die Simulationsergebnisse großen Unsicherheiten, teilweise wegen der geringen Datenverfügbarkeit, andererseits durch die Unsicherheiten in der Modellstruktur zur korrekten Wiedergabe der Sedimentablagerungsprozesse.

The annual and seasonal water use efficiency of six pasture combinations were calculated from the ‘MaxClover’ Grazing Experiment at Lincoln University. Pastures have been established for six years and are grazed by best management practices for each combination. Measurements for this study are from individual plots of four replicates of ryegrass (RG)/white clover (Wc), cocksfoot (CF)/Wc; CF/balansa (Bal) clover; CF/Caucasian (Cc) clover; CF/subterranean (Sub) clover or lucerne. Water extraction measurements showed soils for all dryland pastures had a similar plant available water content of 280±19.8 mm. Dry matter measurements of yield, botanical composition and herbage quality were assessed from 1 July 2008 until 30 June 2009. Lucerne had the highest annual yield of 14260 kg DM/ha/y followed by the CF/Sub at 9390 kg DM/ha/y and the other grass based pastures at ≤ 6900 kg DM/ha/y. All pastures used about 670±24.4 mm/y of water for growth. Lucerne had the highest annual water use efficiency (WUE) of 21 kg DM/ha/mm/y of water used (total yield/total WU). The WUE of CF/Sub was the second highest at 15 kg DM/ha/mm/y, and the lowest was CF/Wc at 9 kg DM/ha/mm/y. The CF/Sub pastures had the highest total legume content of all grass based pastures at 21% and as a consequence had the highest annual nitrogen yield of 190 kg N/ha. This was lower than the monoculture of lucerne (470 kg N/ha). Ryegrass/white clover had the highest total weed component in all pastures of 61%. For dryland farmers spring is vital for animal production when soil temperatures are rising and moisture levels are high. The water use efficiency at this time is important to maximize pasture production. In spring lucerne produced 8730 kg DM/ha, which was the highest dry matter yield of all pastures. The CF/Sub produced the second highest yield of 6100 kg/DM/ha. When calculated against thermal time, CF/Sub grew 5.9 kg DM/ºCd compared with lucerne at 4.9 kg DM/ºCd. The higher DM yield from lucerne was from an extra 400 ºCd of growth. The highest seasonal WUE of all pastures occurred in the spring growing period. Linear regressions forced through the origin, showed lucerne (1/7/08-4/12/08) had a WUE of 30 kg DM/ha/mm (R2=0.98). Of the grass based pastures, CF/Sub produced 18 kg DM/ha/mm (R2=0.98) from 1/7 to 10/11/08 from 270 mm of water used. The lowest spring WUE was 13.5 kg DM/ha/mm by CF/Bal pastures which was comparable to the 14.3±1.42 kg DM/ha/mm WUE of CF/Wc, CF/Cc and RG/Wc pastures. During the spring, CF/Sub clover had the highest spring legume component of the grass based pastures at 42% and produced 120 kg N/ha. This was lower than the 288 kg N/ha from the monoculture of lucerne. Sub clover was the most successful clover which persisted with the cocksfoot. Based on the results from this study dryland farmers should be encouraged to maximize the potential of lucerne on farm, use cocksfoot as the main grass species for persistence, rather than perennial ryegrass, and use subterranean clover as the main legume species in cocksfoot based pastures. By increasing the proportion of legume grown the water use efficiency of a pasture can be improved. When pastures are nitrogen deficient the use of inorganic nitrogen may also improve pasture yields particularly in spring.

The wealth of dryland biodiversity and associated knowledge is poorly documented and as a consequence dryland areas are now a thematic priority of the United Nations Convention on Biological Diversity. A general lack of understanding of the multi-dimensional nature of environmental change and the complexity of these social-ecological systems has fuelled myths about degradation which persist today across Africa. Using a multi-methods approach, this research focuses on biodiversity as a concept through which a more holistic understanding of dynamics might be achieved.

Des études récentes ont montré que les arbres dans les zones arides forment d’importants puits de carbone. On ne connait cependant pas le prix du carbone à partir duquel un agriculteur serait indifférent entre son activité agricole coutumière et une activité de plantation d’arbres. La production de carbone séquestré par les arbres a été simulée sur le modèle CO2FIX v3. 1 pour le pin d’Alep. Les récoltes de blé et la production des pâturages pour les activités agricoles renoncées ont été simulées par des modèles quadratiques semblables, se basant sur les engrais azotés et utilisant 30 ans de données climatiques pour simuler le déficit hydrique. Les deux modèles ont été développés pour les conditions des zones arides. Leur calibrage a été fait sur des données observées en Israël, sur 8 stations, distribuées le long d’un gradient d’aridité (de 200mm à 900mm de précipitation). Les valeurs obtenues pour les récoltes ont été adaptées à une fonction de distribution de probabilité gamma. Les prix de production et de vente, ont eux été adaptés à une distribution normale. Une méthode itérative a permis de simuler l’effet stochastique du prix et du climat sur un flux de trésorerie pendant 30 ans avec 10'000 itérations. Les résultats montrent qu'en dépit de la capacité élevée de l’afforestation dans les zones arides à séquestrer le carbone, son commerce est peu lucratif, quel que soit le niveau d’aridité et l’activité renoncée. En effet, le prix du carbone doit augmenter sensiblement, et les coûts de certifications doivent fortement diminuer, sans quoi, l’afforestation des zones arides dans les pays ne faisant pas partie de l’annexe I ne sera pas un mécanisme adopté
Recent findings demonstrate that dryland trees are efficient carbon sinks. The price of carbon at which a farmer would be indifferent between his customary activity and the plantation of trees for the trade of carbon credits remains however unknown. Carbon yields were simulated by means of the CO2FIX v3. 1 model for Pinus halepensis. Wheat yields and pasture yields were predicted on somewhat similar nitrogen-based quadratic models, using 30 years of weather data for the simulation of moisture stress. Both models were developed for dryland conditions, while calibration and validation were done with data collected in Israel on 8 stations (from 200mm to 900mm of annual precipitation). No-till wheat and pasture yield values were then fitted to a gamma probability distribution function, to enable iterative stochastic production simulation. Input and output prices were, however, fitted to a normal distribution. Stochastic production, input and output prices were afterwards simulated on a Monte Carlo matrix with 10,000 iterations on a 30 years cash flow. Results show that, despite the high levels of carbon uptake by dryland trees, carbon trading by afforesting is unprofitable anywhere along the aridity gradient. Indeed, the price of carbon will have to raise unrealistically high, and the certification costs will have to drop significantly, to make afforestation under the clean development mechanism a worthwhile activity for non annex I dryland countries

Australia is experiencing widespread ecosystem degradation, including dryland salinity, erosion and vegetation loss. Approximately 1 million hectares (5.5%) of the south-west agricultural zone of Western Australia is affected by dryland salinity and is predicted to rise to 5.4 million hectares by 2050. Such degradation is associated with many environmental outcomes that may impact on human health, including a decrease in primary productivity, an increase in the number of invasive species, a decrease in the number of large trees, overall decrease in biodiversity, and an increase in dust production. The resulting degradation affects not only farm production but also farm values. This study examines the effects of such severe and widespread environmental degradation on the physical and mental health of residents. Western Australia has an extensive medical record database which links individual health records for all hospital admissions, cancer cases, births and deaths. For the 15 diseases examined in this project, the study area of the south west of Western Australia (excluding the capital city of Perth) contained 1,570,985 morbidity records and 27,627 mortality records for the 15 diseases examined in a population of approximately 460,000. Environmental data were obtained from the Western Australian Department of Agriculture?s soil and landscape mapping database. A spatial Bayesian framework was used to examine associations between these disease and environmental variables. The Bayesian model detected the confounding variables of socio-economic status and proportion of the population identified as Aboriginal or Torres Strait Islander. With the inclusion of these confounders in the model, associations were found between environmental degradation (including dryland salinity) and several diseases with known environmentally-mediated triggers, including asthma, ischaemic heart disease, suicide and depression. However, once records of individuals who had been diagnosed with coexistent depression were removed from the analysis, the effect of dryland salinity was no longer statistically detectable for asthma, ischaemic heart disease or suicide, although the effects of socio-economic status and size of the Aboriginal population remained. The spatial component of this study showed an association between land degradation and human health. These results indicated that such processes are driving the degree of psychological ill-health in these populations, although it remains uncertain whether this 4 is secondary to overall coexisting rural poverty or some other environmental mechanism. To further investigate this complex issue an instrument designed to measure mental health problems in rural communities was developed. Components of the survey included possible triggers for mental health, including environmental factors. The interview was administered in a pilot study through a telephone survey of a small number of farmers in South-Western Australia. Using logistic regression a significant association between the mental health of male farmers and dryland salinity was detected. However, the sample size of the survey was too small to detect any statistically significant associations between dryland salinity and the mental health of women. The results of this study indicate that dryland salinity, as with other examples of ecosystem degradation, is associated with an increased burden of human disease.

Maintaining phosphorus (P) fertility in northern Great Plains (NGP) dryland organic cropping systems is a challenge due to high pH, calcareous soils that limit P bioavailability. Organic P fertilizers, including rock phosphate (RP) and bone meal (BM) are sparingly soluble in higher pH soils. Certain crops species have demonstrated an ability to mobilize sparingly soluble P sources. Objectives of this project were to 1) evaluate the effect of green manure (GM) crops and organic P fertilizers on the P nutrition of subsequent crops, and 2) investigate P fertility differences between organic and non-organic cropping systems. A two-year cropping sequence was conducted on an organic farm in north-central Montana (mean pH=6.6; Olsen P=16 mg kg⁻¹). Spring pea (Pisum sativum L), buckwheat (Fagopyrum esculentum L.), yellow mustard (Sinapis alba L.) and tilled fallow were fertilized with 0, 3.1 and 7.7 kg P ha⁻¹ as RP, grown to flat pod stage and terminated with tillage. Winter wheat (Triticum aestivum L.) was grown on these plots in year two. Phosphorus uptake of winter wheat was enhanced (P>0.05) by RP following buckwheat only (P=0.02) at 7.7 kg P ha⁻¹ compared to 0 P. Results indicate buckwheat can enhance P in a subsequent crop. A greenhouse pot experiment in a low P soil (Olsen P=4 mg kg⁻¹) consisted of four green manures; buckwheat, spring pea, wheat, and a non-crop control fertilized with 7.0 and 17.5 kg available P ha⁻¹ as RP, 13.0 and 32.5 kg available P ha⁻¹ as BM and 10 and 25 kg available P ha⁻¹ as monocalcium phosphate (MCP). Green manures were harvested, dried, analyzed for nutrient content, and returned to pots. Pots were seeded with wheat. Phosphorus uptake in wheat following all crops was enhanced by MCP (P<0.05). Phosphorus uptake of wheat following buckwheat was enhanced by all P sources over the control. Buckwheat demonstrates the capacity to increase the availability of organic P fertilizers. Soil sampling of organic and non-organic no-tillage (NT) cropping systems was conducted in two separate studies to determine differences in P availability between management systems. Soil analysis determined available P tends to be lower in non-fertilized systems.

Drylands cover nearly half of the earth’s terrestrial surface and are home to unique ecosystems and vibrant cultures. Dryland communities face various challenges of living in the harsh and variable conditions presented by their environment and landscapes. These challenges are magnified in the arid landscapes of India, where agriculture is largely rain-fed and human and livestock population densities are some of the largest in the world. Communities and landscapes in arid India are exceptionally vulnerable due to intensifying dryland degradation, increasing rainfall variability along with climate change. This thesis contributes to a critical research area by developing and applying a methodological framework centred on ‘vulnerability’ for investigating dryland degradation in India’s arid landscapes. Dryland degradation is studied as a synthesis of the complex interactions between socio-ecological system functions within inherently dynamic environments. The empirical basis for the study is the use of mixed methods incorporating primary and secondary data, enriched by community perspectives. The study provides new insights through findings on the interactions between land use, land degradation, and climate risks. It addresses gaps in drylands research, especially in the development of a context specific vulnerability framework for drylands. It, furthermore, uses this framework to provide recommendations to confront dryland degradation while planning for effective adaptation. Overall, the analysis finds that the dominant narrative in India - of poor farmers in the Thar desert struggling to cope with drought, in need of protection from their natural environment – to be fundamentally misplaced. However, as their land becomes increasingly degraded and their surrounding climate less predictable, their socio-cultural systems and institutions become less resilient. As a result, arid zone farmers are now more likely to turn to strategies that aim for short-term solutions, which may only exacerbate vulnerability and land degradation in the longer term.

[Truncated abstract] In an era of emerging and resurging infectious diseases, understanding the ecological processes that influence pathogen activity and the influences of anthropogenic change to those are critical. Ross River virus (RRV, Togoviridae: Alphavirus) is a mosquito-borne zoonosis occurring in Australia with a significant human disease burden. In the southwest of Western Australia (WA) RRV is principally vectored by Aedes camptorhynchus Thomson (Diptera: Culicidae), which is halophilic. The inland southwest, the Wheatbelt region, of WA is substantially affected by an anthropogenic salinisation of agricultural land called dryland salinity, which threatens to influence transmission of this arbovirus. This study assessed the ecological impacts of dryland salinity on mosquitoes, mammalian hosts and their interactions to influence the potential for RRV transmission. Many aquatic insect taxa colonise ephemeral water bodies directly as adults or by oviposition. Using a manipulative experiment and sampling from ephemeral water bodies in the Wheatbelt, I demonstrated that salinity of water bodies can modify colonisation behaviour and the distribution of some organisms across the landscape. Halosensitive fauna selected less saline mesocosms for oviposition and colonisation. In particular, Culex australicus Dobrotworksy and Drummond and Anopheles annulipes Giles (Diptera: Culicidae), potential competitors with Ae. camptorhynchus, avoided ovipostion in saline mesocosms and water bodies in the field. This finding suggests salinity influences behaviour and may reduce interspecific interactions between these taxa and Ae. camptorhynchus at higher salinities. Using extensive field surveys of ephemeral water bodies in the Wheatbelt I found mosquitoes frequently colonised ephemeral water bodies, responded positively to rainfall, and populated smaller water bodies more densely than larger water bodies. The habitat characteristics of ephemeral water bodies changed in association with salinity. Consequently there were both direct and indirect associations between salinity and colonising mosquitoes. Ultimately the structure of mosquito assemblages changed with increasing salinity, favouring an increased regional distribution and abundance of Ae. camptorhynchus. The direct implication of this result is secondary salinisation has enhanced the vectorial potential for RRV transmission in the WA Wheatbelt. ... This thesis contributes to an emerging body of research aimed at delineating important ecological processes which determine transmission of infections disease. Collectively the findings in this study suggest dryland salinity enhances the potential for RRV activity in the Wheatbelt. Currently, human RRV notifications in the Wheatbelt do not reflect the salinity-RRV transmission potential in that area, but appear to be associated with dispersal of RRV from the enzootic coastal zone of southwest WA. I speculate dryland salinity is a determinant of potential for RRV transmission, but not activity. Dryland salinity is predicted to undergo a two to four fold expansion by 2050, which will increase the regional potential for RRV activity. Preservation and restoration of freshwater ecosystems may ameliorate the potential for transmission of RRV and, possibly, human disease incidence.

[Truncated abstract] The salinisation of agricultural land, urban infrastructure and natural habitat is a serious and increasing problem in southern Australia. Government funding has been allocated to the problem to attempt to reduce substantial costs associated with degradation of agricultural and non-agricultural assets. Nevertheless, Government funding has been small relative to the size of the problem and therefore expenditure needs to be carefully targeted to interventions that will achieve the greatest net benefits. For intervention to be justified, the level of salinity resulting from private landholder decisions must exceed the level that is optimal from the point of view of society as a whole, and the costs of government intervention must be less than the benefits gained by society. This study aims to identify situations when government intervention is justified to manage dryland salinity that threatens to affect road infrastructure (a public asset). A key gap in the environmental economics literature is research that considers dryland salinity as a pollution that has off-site impacts on public assets. This research developed two hydrological/economic models to achieve this objective. The first was a simple economic model representing external costs from dryland salinity. This model was used to identify those variables that have the biggest impact on the net-benefits possible from government intervention. The second model was a combined hydro/economic model that represents the external costs from dryland salinity on road infrastructure. The hydrological component of the model applied the method of metamodelling to simplify a complex, simulation model to equations that could be easily included in the economic model. The key variables that have the biggest impact on net-benefits of dryland salinity mitigation were the value of the off-site asset and the time lag before the onset of dryland salinity in the absence of intervention. ... In the case study of dryland salinity management in the Date Creek subcatchment of Western Australia, the economics of vegetation-based and engineering strategies were investigated for road infrastructure. In general, the engineering strategies were more economically beneficial than vegetation-based strategies. In the case-study catchment, the cost of dryland salinity affecting roads was low relative to the cost to agricultural land. Nevertheless, some additional change in land management to reduce impacts on roads (beyond the changes justified by agricultural land alone) was found to be optimal in some cases. Reinforcing the results from the simple model, a key factor influencing the economics of dryland salinity management was the urgency of the problem. If costs from dryland salinity were not expected to occur until 30 years or more, the optimal response in the short-term was to do nothing. Overall, the study highlights the need for governments to undertake comprehensive and case-specific analysis before committing resources to the management of dryland salinity affecting roads. There were many scenarios in the modelling analysis where the benefits of interventions would not be sufficient to justify action.

What enables a community to cope with stress, to recover from trauma, and to provide the next generation with the opportunity for a sustainable livelihood? What makes a community vulnerable to, and lack the capacity to sustain livelihoods? This thesis is a case study of three subsistence communities in semi-arid West Timor, Indonesia, that belong to the Atoin Meto tribal group. While climatic hazards can leave a community vulnerable, there are other underlying factors, particularly in rural West Timor, where the societal structure has failed to protect all members of the society adequately. This thesis seeks to understand the problem of what causes vulnerability to the livelihood of these communities in the era of global warming, and why their societal structure is unable to protect all members adequately in this circumstance. Since the aftermath of WWII, the welfare of the rural poor in developing countries has not substantially improved (Griffin & Khan 1978; Streeten 1984; Chambers 1995) exacerbated by environmental and developmental problems which have arisen due to the disconnections between the policy makers, the rural poor and their environment (Agarwal & Narain 1985). In the era of global warming, communities in rural drylands will be the most vulnerable group (Solomon et al. 2007; Fraser et al. 2011). A critical assessment is therefore needed to discover the real problems experienced in rural dryland regions in order to empower the local people and support their livelihoods in the future.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith Business School
Griffith Business School
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Thesis (M.Sc (Plant Production)) --University of Limpopo, 2015
Information on the performance of the maize and pigeonpea intercropping system under dryland conditions of South Africa is scanty. The aim of this study was to determine the optimum P level and productivity of pigeonpea and maize under the dryland intercropping system. Five P rates (0, 15, 30, 45, and 60 kg P ha-1) were applied to both sole and pigeonpea intercropped with maize in a randomized complete block design with 4 replicates. Growth parameters and yield and yield attributes of pigeonpea and maize were measured to determine performance of both crops. There were significant differences in grain yield of pigeonpea as influenced by P rates in both seasons. Highest grain yields of 781 kg ha-1 during 2009/10 and 894 kg ha-1 during 2010/11 were obtained at P rate of 45 kg ha-1. Cropping system significantly influenced grain yield of pigeonpea in 2010/11 season with 37.1% higher pigeonpea grain yield from intercropped plots than in sole pigeonpea plots. There was 21.8% increase in grain yield of pigeonpea across two seasons as influenced by P rate. Maize grain yield showed little response to P rate only during the first season. However, highest maize grain yield of 1699 kg ha-1 was obtained at 60 kg P ha-1 during the 2009/10 season. Maize grain yield was only significantly influenced by cropping system during the 2010/11 season where sole plots achieved higher grain yield of 4148 kg ha-1 compared to 3297 kg ha-1 from intercrop plots. The results revealed that P application increased grain yield of pigeonpea significantly, especially in intercropped plots. The calculated total land equivalent ratio (LER) for the two crops gave positive and higher than one values, which suggests a favourable grain yield advantage for maize/pigeon pea intercrop.

The pronounced constraints on ecosystem functioning and human livelihoods in drylands are frequently exacerbated by natural and socio-economic stresses, including weather extremes and inequitable trade conditions. Therefore, a better understanding of the relation between these stresses and the socio-ecological systems is important for advancing dryland development. The concept of vulnerability as applied in this dissertation describes this relation as encompassing the exposure to climate, market and other stresses as well as the sensitivity of the systems to these stresses and their capacity to adapt. With regard to the interest in improving environmental and living conditions in drylands, this dissertation aims at a meaningful generalisation of heterogeneous vulnerability situations. A pattern recognition approach based on clustering revealed typical vulnerability-creating mechanisms at global and local scales. One study presents the first analysis of dryland vulnerability with global coverage at a sub-national resolution. The cluster analysis resulted in seven typical patterns of vulnerability according to quantitative indication of poverty, water stress, soil degradation, natural agro-constraints and isolation. Independent case studies served to validate the identified patterns and to prove the transferability of vulnerability-reducing approaches. Due to their worldwide coverage, the global results allow the evaluation of a specific system’s vulnerability in its wider context, even in poorly-documented areas. Moreover, climate vulnerability of smallholders was investigated with regard to their food security in the Peruvian Altiplano. Four typical groups of households were identified in this local dryland context using indicators for harvest failure risk, agricultural resources, education and non-agricultural income. An elaborate validation relying on independently acquired information demonstrated the clear correlation between weather-related damages and the identified clusters. It also showed that household-specific causes of vulnerability were consistent with the mechanisms implied by the corresponding patterns. The synthesis of the local study provides valuable insights into the tailoring of interventions that reflect the heterogeneity within the social group of smallholders. The conditions necessary to identify typical vulnerability patterns were summarised in five methodological steps. They aim to motivate and to facilitate the application of the selected pattern recognition approach in future vulnerability analyses. The five steps outline the elicitation of relevant cause-effect hypotheses and the quantitative indication of mechanisms as well as an evaluation of robustness, a validation and a ranking of the identified patterns. The precise definition of the hypotheses is essential to appropriately quantify the basic processes as well as to consistently interpret, validate and rank the clusters. In particular, the five steps reflect scale-dependent opportunities, such as the outcome-oriented aspect of validation in the local study. Furthermore, the clusters identified in Northeast Brazil were assessed in the light of important endogenous processes in the smallholder systems which dominate this region. In order to capture these processes, a qualitative dynamic model was developed using generalised rules of labour allocation, yield extraction, budget constitution and the dynamics of natural and technological resources. The model resulted in a cyclic trajectory encompassing four states with differing degree of criticality. The joint assessment revealed aggravating conditions in major parts of the study region due to the overuse of natural resources and the potential for impoverishment. The changes in vulnerability-creating mechanisms identified in Northeast Brazil are well-suited to informing local adjustments to large-scale intervention programmes, such as “Avança Brasil”. Overall, the categorisation of a limited number of typical patterns and dynamics presents an efficient approach to improving our understanding of dryland vulnerability. Appropriate decision-making for sustainable dryland development through vulnerability reduction can be significantly enhanced by pattern-specific entry points combined with insights into changing hotspots of vulnerability and the transferability of successful adaptation strategies.
Die Grenzen ökologischer Funktionen und menschlicher Lebensweisen in Trockengebieten werden häufig durch natürlichen und sozio-ökonomischen Stress, wie extreme Wetterereignisse und ungerechte Handelsbedingungen, weiter verengt. Zur Förderung der Entwicklung in Trockengebieten ist es daher wichtig, die Beziehung zwischen den Stressfaktoren und den sozio-ökologischen Systemen besser zu verstehen. Das Konzept der Vulnerabilität, welches in der vorliegenden Dissertation angewandt wird, beschreibt dieses Verhältnis durch die Exposition, Sensitivität und Anpassungsfähigkeit von Systemen im Hinblick auf Klima-, Markt- und anderen Stress. Bezüglich des Interesses, die Umwelt- und Lebensbedingungen in Trockengebieten zu verbessern, zielt diese Dissertation darauf ab, die vielschichtigen Ursachen und Veränderungen von Vulnerabilität sinnvoll zu verallgemeinern. Eine clusterbasierte Mustererkennung zeigte typische Mechanismen auf, welche Vulnerabilität auf globaler und lokaler Ebene verursachen. Dabei stellt die globale Studie die erste flächendeckende Untersuchung von Vulnerabilität in Trockengebieten mit sub-nationaler Auflösung dar. Die Clusteranalyse identifizierte sieben typische Muster basierend auf der quantitativen Beschreibung von Armut, Wasserknappheit, Bodendegradation, natürlichen Produktionshemmnissen und Isolation. Die Gültigkeit der ermittelten Cluster und die Übertragbarkeit von Anpassungsmaßnahmen innerhalb ähnlicher Gebiete wurden anhand unabhängiger Fallstudien belegt. Die flächendeckende Erfassung erlaubt es, die Vulnerabilität eines Systems in seinem größeren Kontext zu bewerten, auch in weniger gut durch Fallstudien dokumentierten Gebieten. Weiterhin wurde die Klimavulnerabilität von Kleinbauern bezüglich ihrer Nahrungsmittelsicherung im peruanischen Altiplano untersucht. In diesem lokalen Kontext wurden vier Cluster von Haushalten gemäß ihrer Produktionsrisiken, landwirtschaftlichen Ressourcen, der Bildung und ihres nicht-landwirtschaftlichen Einkommens unterschieden. Eine erweiterte Gültigkeitsprüfung unter Nutzung unabhängig erhobener Informationen stellte heraus, dass wetterbedingte Schäden mit den ermittelten Clustern korrelieren und dass haushaltsspezifische Schadensursachen mit den durch die Muster angezeigten Mechanismen übereinstimmen. Die lokale Studie liefert wertvolle Hinweise auf bedarfsgerechte Eingriffe unter Beachtung der Heterogenität innerhalb der sozialen Gruppe der Kleinbauern. Die notwendigen Bedingungen zur Erkennung typischer Muster ergaben fünf methodische Schritte. Ihre Darlegung soll die Anwendung der gewählten Methode in zukünftigen Vulnerabilitätsstudien anregen und erleichtern. Die fünf Schritte umfassen die Ableitung relevanter Ursache-Wirkungs-Hypothesen, die Quantifizierung der Mechanismen, die Bewertung von Robustheit und Gültigkeit sowie die Ordnung der ermittelten Muster nach dem Grad der Vulnerabilität. Dabei ist die genaue Beschreibung der Hypothesen eine wesentliche Voraussetzung für die Quantifizierung der grundlegenden Prozesse sowie eine einheitliche Interpretation, Gültigkeitsprüfung und Ordnung der ermittelten Muster. Besondere Beachtung finden skalenbedingte Aspekte, wie beispielsweise die ergebnisorientierte Gültigkeitsprüfung in der lokalen Studie. Weiterhin wurden die in Nordostbrasilien ermittelten Cluster im Hinblick auf wichtige endogene Prozesse in den dort vorherrschenden kleinbäuerlichen Nutzungssystemen untersucht. Diese Prozesse umfassen die Aufteilung der Arbeitskraft, die landwirtschaftliche Produktion sowie Einkommens- und Ressourcendynamiken. Sie wurden in einem qualitativen dynamischen Modell erfasst, welches eine zyklische Trajektorie mit vier unterschiedlich problematischen Entwicklungszuständen ergab. Als besonders problematischer Aspekt verschärfte sich die Vulnerabilität in weiten Teilen des Untersuchungsgebietes durch die Übernutzung natürlicher Ressourcen und die Möglichkeit weiterer Verarmung. Die in Nordostbrasilien gezeigten Veränderungen sind dazu geeignet, groß angelegte Entwicklungsprogramme, wie zum Beispiel “Avança Brasil”, angemessen an lokale Gegebenheiten anzupassen. Insgesamt ermöglicht es die Kategorisierung einer begrenzten Anzahl typischer Muster und Veränderungen, die Vulnerabilität in Trockengebieten besser zu verstehen. Eine nachhaltige Entwicklung von Trockengebieten basierend auf der Minderung von Vulnerabilität kann durch musterspezifische Ansätze zusammen mit Hinweisen zu Veränderungen im Schweregrad und zur Übertragbarkeit erfolgreicher Anpassungsstrategien wirkungsvoll unterstützt werden.

Riverine landscapes are complex. More than just a single channel, they comprise a shifting mosaic of hydrogeomorphic patches with varying physical and biological characteristics. These patches are connected by water during flows of varying magnitude and frequency, at a range of spatial and temporal scales. Combined, landscape complexity and hydrological connectivity create biological diversity that in turn maintains the productivity, ecological function, and resilience of these systems. This thesis investigates the ecological importance of spatial heterogeneity and temporal hydrological connectivity in a dryland floodplain river landscape. It focuses on anabranch channels, and uses major carbon sources in these and adjacent landscape patches as indicators of ecological pattern and process. A conceptual model was proposed, describing the potential effects upon the distribution and availability of major carbon sources of: a) a spatial mosaic of hydrogeomorphic patches in the landscape (e.g. anabranches, river channel, and wider floodplain); and b) four primary temporal phases of hydrological connection during flow pulses (disconnection, partial connection, complete connection, and draining). This was then tested by data collected over a three year period from a 16 km reach of the lower Macintyre River (NSW/QLD Australia). Results were examined at multiple spatial scales (patch scale � river channel vs. anabranches vs. floodplain; between individual anabranches; and within anabranches � entry, middle and exit sites). The data indicate that spatial heterogeneity in the lower Macintyre River landscape significantly influences ecological pattern. Carbon quantity was greater in anabranch channels compared to adjacent river channel patches, but not compared to the floodplain; while carbon quality was greater in anabranch channels compared to both adjacent river channel and floodplain patches. Stable isotope analysis indicated that carbon sources that were predominantly found in anabranch channels supported both anabranch and river organisms during a winter disconnection phase. Other carbon sources found in the main river channel and the wider floodplain appeared to play a comparatively minimal role in the food web. Different phases of hydrological connection between anabranch channels and the main river channel were associated with differences in the availability of carbon sources. In the river channel, draining of water from anabranches (the draining phase) was associated with relatively high concentrations of dissolved organic carbon (DOC) and low concentrations of phytoplankton. Conversely, the disconnection phase was associated with relatively low concentrations of DOC and high concentrations of phytoplankton in the river channel. In anabranch channels and their waterbodies, the disconnection and draining phases were associated with high concentrations of both DOC and phytoplankton. Concentrations of these carbon sources were lowest in anabranches during the partial and complete connection phases. Different hydrological connection phases were also associated with changes in trophic status in the aquatic components of the landscape. On the riverbanks, relatively low rates of benthic production and respiration during the complete connection phase were associated with heterotrophy. The remaining phases appeared to be autotrophic. Benthic production on riverbanks was greatest during the disconnection phase, and respiration was greatest during the partial connection phase. In the anabranch channels, rates of production and respiration were similar during the disconnection phase, and were associated with heterotrophy in the anabranch waterbodies. The remaining phases appeared to be autotrophic. Respiration was greatest in anabranches during the disconnection phase, and production was greatest during the draining phase. Both production and respiration were lowest during complete connection. These differences and changes varied according to the landscape patch examined. At a landscape scale, anabranch channels act as both sinks and suppliers of carbon. High rates of sediment deposition facilitate their role as sinks for sediment-associated carbon and other particulate, refractory carbon sources. Simultaneously, anabranch channels supply aquatic carbon sources from their waterbodies, as well as via processes such as inundation-stimulated release of DOC from surface sediments. Modelled data indicated that water resource development reduces the frequency and duration of connection between anabranch channels and the main river channel. This loss of landscape complexity via loss of connectivity with anabranches has the potential to reduce the total availability of carbon sources to the ecosystem, as demonstrated by a modelled 13% reduction in potential dissolved organic carbon release from anabranch sediments. This thesis has demonstrated the importance of spatial heterogeneity in riverine landscapes, by documenting its association with variability in the distribution and quality of primary energy sources for the ecosystem. It has shown that this variability is augmented by different phases of hydrological connectivity over time. Spatial heterogeneity and hydrological connectivity interact to increase the diversity and availability of ecological energy sources across the riverine landscape, at multiple spatial and temporal scales. This has positive implications for the resilience and sustainability of the system. Anabranch channels are particularly important facilitators of these effects in this dryland floodplain river system. Anabranch channels are �intermediate� in terms of spatial placement, temporal hydrological connection, and availability of carbon sources; of high value in terms of high-quality carbon sources; and relatively easy to target for management because of their defined commence-to-flow levels. Further research should be directed toward evaluating other ecological roles of anabranch channels in dryland rivers, thereby providing a more complete understanding of the importance of connectivity between these features and other patches. This knowledge would assist management of floodplain river landscapes at larger regional scales, including amelioration of the effects of water resource development.

Existing facies models of rift basin evolution are biased towards humid climatic regimes. This study uses geomorphic and sedimentologic observations from the actively extending, arid to semi-arid Basin and Range Province, Western U.S.A., to critically assess the applicability of the existing models to dryland regions. This was achieved by documenting the range of landscape responses to extensional tectonism in drylands, with the subsequent development of a revised, dryland specific, extensional basin facies evolution model. The geomorphic and sedimentologic character of six representative modern basins was mapped, and their facies proportions calculated. Key observations are the rarity of well-integrated exogenic fluvial systems and the resulting dominance of sediments issuing out of transverse catchments. The landscape maturity of the basins was quantified in order to compare their facies distributions within an evolutionary framework, serving as a proxy for rift phase. Syn to post rift facies evolution is characterised by: 1) a progression with drainage evolution from mixed debris and stream flow to stream flow dominated processes in marginally derived alluvium; 2) the inundation of playa facies as marginal facies prograde into increasingly central positions; 3) the resultant loss of facies asymmetry; 4) increasingly homogenised basinal facies, as longer sediment residence times at the surface allow for greater potential reworking; 5) a reduction in marginal catchment relief. Observations from the modern basins were tested against the Miocene to Recent post rift basin fill of the Virgin River Depression. Existing models suggest the dominance of axial fluvial sedimentation throughout the life of extensional basins. Findings of this study show that longitudinal fluvial sedimentation in dryland basins is, however, limited and if present, more likely to be restricted to the later, post rift stages of basin evolution.

This dissertation investigated the practicality and expediency of applying remote sensing data fusion products to the analysis of dryland vegetation phenology. The objective of the first study was to verify the quality of the output products of the spatial and temporal adaptive reflectance fusion method (STARFM) over the dryland Arizona study site. Synthetic 30 m resolution images were generated from Landsat-5 Thematic Mapper (TM) data and a range of 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance datasets and assessed via correlation analysis with temporally coincident Landsat-5 imagery. The accuracy of the results (0.61 < R2 < 0.94) justified subsequent use of STARFM data in this environment, particularly when the imagery were generated from Nadir Bi-directional Reflectance Factor (BRDF)-Adjusted Reflectance (NBAR) MODIS datasets. The primary objective of the second study was to assess whether synthetic Landsat data could contribute meaningful information to the phenological analyses of a range of dryland vegetation classes. Start-of-season (SOS) and date of peak greenness phenology metrics were calculated for each STARFM and MODIS pixel on the basis of enhanced vegetation index (EVI) and normalized difference vegetation index (NDVI) time series over a single growing season. The variability of each metric was calculated for all STARFM pixels within 500 m MODIS extents. Colorado Plateau Pinyon Juniper displayed high amounts of temporal and spatial variability that justified the use of STARFM data, while the benefit to the remaining classes depended on the specific vegetation index and phenology metric. The third study expanded the STARFM time series to five years (2005-2009) to examine the influence of site characteristics and climatic conditions on dryland ponderosa pine (Pinus ponderosa) forest phenological patterns. The results showed that elevation and slope controlled the variability of peak timing across years, with lower elevations and shallower slopes linked to higher levels of variability. During drought conditions, the number of site variables that controlled the timing and variability of vegetation peak increased.
Ph. D.

Drylands represent the planet's largest terrestrial biome and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts). soil surface communities of lichens, mosses, and/or cyanobacteria. comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness-changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+ 4 degrees C above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (> 30%). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate.

Australia’s largest and most important waterway- the Murray-Darling Basin (MDB) - is under threat owing to predicted increases in temperature extremes and reduction in rainfall - runoff in the coming decades. Management strategies are required that incorporate an understanding of dispersal patterns of the MDB fauna and flora. Patterns of dispersal have typically been studied through direct organismal studies but genetic approaches, in which the movement of genes in the landscape is used as a correlate of species dispersal, can provide a more comprehensive view by investigating at a much larger temporal and spatial scale. Genetic connectivity (dispersal) is influenced by the biology of the species, and by flow regime and the dendritic pattern of the network in riverine landscapes. An understanding of the relative influence of each on connectivity is required to deliver informed management strategies. Decisions regarding whether management for conservation is necessary also require an understanding of a species susceptibility to a changing environment. Species already exhibiting deleterious trajectories under current flow regimes in the basin may require more drastic measures than those that have remained unaffected.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

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

Wheat consumption has become more widespread and is increasing in South Africa especially in the urban areas. The wheat industry contributes four billion rands to the gross value of agriculture and is a source of employment to approximately 28 000 people. Wheat yield forecasting is crucial in planning for imports and exports depending on the expected yields and wheat health monitoring is important in minimizing crop losses. However, current crop surveying techniques used in South Africa rely on manual field surveys and aerial surveys, which are costly and not timely (after harvest). This research focuses on wheat health monitoring and wheat yield prediction using remote sensing, which is a cost effective, reliable and time saving alternative to manual surveys. Hence, the research objectives were: (i) to identify remotely sensed spectral indices that comprehensively describe wheat health status. (ii) Develop an Normalized Difference Vegetation Index (NDVI) based wheat yield forecasting model and (iii) to evaluate the impact of selected agrometeorological parameters on the NDVI based forecasting model. Landsat 8 images were used for determining spectral indices suitable for wheat health monitoring by relating the spectral indices to the land surface temperature. Results show that the Normalized Difference Water Index (R2 between 0.65 and 0.89) and NDVI (R2 between 0.36 and 0.62) were the most suitable indices for wheat health status monitoring. Whereas, the Normalized Difference Moisture Index (R2 between 0.53 and 0.79) and the Green Normalized Difference Vegetation Index (R2 between 0.28 and 0.41) were found to be less suitable for wheat health monitoring. Moderate Resolution Spectroradiometer (MODIS) derived NDVI for fourteen years was used to build and test a wheat yield forecasting model. The model was significant with an R2 value of 0.73, a p-value of 0.00161 and an RMSE of 0.41 tons ha-1. The study established that the period 30 days before harvest during the anthesis growth stage, is the best period to use the linear regression model for wheat yield forecasting. Satellite derived agrometeorological parameters such as: soil moisture, evapotranspiration and land surface temperature were added to the NDVI based model to form a multi-linear regression model. The addition of these parameters to the NDVI model improved it from an R2 of 0.73 to an R2 of 0.82. Through the use of a correlation matrix, the NDVI (r=0.88) and evapotranspiration (r=0.58) were highly correlated to wheat yield as compared to soil moisture (r=0.27) and land surface temperature (r=-0.02). This research provided evidence that remote sensing can be used at acceptable levels of accuracy for wheat monitoring and wheat yield predictions compared to manual field surveys which are costly and time consuming.
Dissertation (MSc)--University of Pretoria, 2017.
Agricultural Research Council
National Research Foundation
Spatial Business IQ
GeoTerra Images
University of Pretoria
Geography, Geoinformatics and Meteorology
MSc
Unrestricted

The purpose of this study was to determine the economic viability of various dryland wheat tillage systems, many of which were developed from years of cooperative research efforts. In the study three conventional tillage methods were analyzed along with ten conservation tillage practices. The study farm consisted of 2000 acres, of which 1000 acres are classified as land 1 and its wheat yield is assumed to be 35 bushels per acre for non-continuous tillage methods and 23 bushels per acre for continuous tillage methods. The remaining 1000 acres are classed as land 2 and its assumed wheat yield is 30 bushels per acre for non-continuous tillage methods and 20 bushels per acre for continuous tillage practices. The farm operating conditions were changed to allow for an economic evaluation of questions that a dryland farmer would face. Questions such as: 1. do no-till chemical-fallow treatments have higher profits than do conventional tillage treatments; 2. will it pay for my farming enterprise to participate in the 1990 Farm Bills' Acreage Reduction Program (ARP); 3. what effect will be on returns to land, labor and management of a new 20-ft combine purchase, were analyzed using the Cost and Return Estimator (CARE) computer enterprise budgeting program developed for USDA-Soil Conservation Service (SCS) for each land class totaling 104 CARE budgets. A computer linear programming optimization model was run using LINDO to examine the 104 CARE budgets for an optimal tillage practice. The results are as follows: 1. Under the study assumptions chemical-fallow (no-till) treatments have higher profits than do conventional tillage treatments, if conventional tillage equipment can be adapted to no-till tillage methods. 2. Participation in the government ARP set-aside will offset the higher machinery ownership costs and thus it would pay to participate. 3 . The purchase of a new 20-ft combine or no-till Yielder drill as well as other major purchases could bankrupt a farming enterprise. It should be handled with CARE.

Pattern formation and modulation is an active branch of mathematics, not only from the perspective of fundamental theory but also for its huge applications in many fields of physics, ecology, chemistry, biology, and other sciences. In this thesis, the occurrence of Turing and wave instabilities, giving rise to stationary and oscillatory patterns, respectively, is theoretically investigated by means of two-compartment reaction-transport hyperbolic systems. The goal is to elucidate the role of inertial times, which are introduced in hyperbolic models to account for the finite-time propagation of disturbances, in stationary and transient dynamics, in supercritical and subcritical regimes. In particular, starting from a quite general framework of reaction-transport model, three particular cases are derived. In detail, in the first case, the occurrence of stationary patterns is investigated in one-dimensional domains by looking for the inertial dependence of the main features that characterize the formation and stability process of the emerging patterns. In particular, the phenomenon of Eckhaus instability, in both supercritical and subcritical regimes, is studied by adopting linear and multiple-scale weakly-nonlinear analysis and the role played by inertia during the transient regime, where an unstable patterned state evolves towards a more favorable stable configuration through sequences of phase-slips, is elucidated. Then, in the second topic, the focus is moved to oscillatory periodic patterns generated by wave (or oscillatory Turing) instability. This phenomenon is studied by considering 1D two-compartment hyperbolic reaction-transport systems where different transport mechanisms of the species here involved are taken into account. In these cases, by using linear and weakly nonlinear stability analysis techniques, the dependence of the non-stationary patterns on hyperbolicity is underlined at and close to the criticality. In particular, it is proven that inertial effects play a role, not only during transient regimes from the spatially-homogeneous steady state toward the patterned state but also in altering the amplitude, the wavelength, the migration speed, and even the stability of the travelling waves. Finally, in the last case, the formation and stability of stationary patterns are investigated in bi-dimensional domains. To this aim, a general class of two-species hyperbolic reaction-transport systems is deduced following the guidelines of Extended Thermodynamics theory. To characterize the emerging Turing patterns, linear and weakly nonlinear stability analysis on the uniform steady states are addressed for rhombic and hexagonal planform solutions. In order to gain some insight into the above-mentioned dynamics, the previous theoretical predictions are corroborated by numerical simulations carried out in the context of dryland ecology. In this context, patterns become a relevant tool to identify early warning signals toward desertification and to provide a measure of resilience of ecosystems under climate change. Such ecological implications are discussed in the context of the Klausmeier model, one of the easiest two-compartment (vegetation biomass and water) models able to describe the formation of patterns in semi-arid environments. Therefore, it will be also here discussed how the experimentally-observed inertia of vegetation affects the formation and stability of stationary and oscillatory periodic vegetation patterns.
Pattern formation and modulation is an active branch of mathematics, not only from the perspective of fundamental theory but also for its huge applications in many fields of physics, ecology, chemistry, biology, and other sciences. In this thesis, the occurrence of Turing and wave instabilities, giving rise to stationary and oscillatory patterns, respectively, is theoretically investigated by means of two-compartment reaction-transport hyperbolic systems. The goal is to elucidate the role of inertial times, which are introduced in hyperbolic models to account for the finite-time propagation of disturbances, in stationary and transient dynamics, in supercritical and subcritical regimes. In particular, starting from a quite general framework of reaction-transport model, three particular cases are derived. In detail, in the first case, the occurrence of stationary patterns is investigated in one-dimensional domains by looking for the inertial dependence of the main features that characterize the formation and stability process of the emerging patterns. In particular, the phenomenon of Eckhaus instability, in both supercritical and subcritical regimes, is studied by adopting linear and multiple-scale weakly-nonlinear analysis and the role played by inertia during the transient regime, where an unstable patterned state evolves towards a more favorable stable configuration through sequences of phase-slips, is elucidated. Then, in the second topic, the focus is moved to oscillatory periodic patterns generated by wave (or oscillatory Turing) instability. This phenomenon is studied by considering 1D two-compartment hyperbolic reaction-transport systems where different transport mechanisms of the species here involved are taken into account. In these cases, by using linear and weakly nonlinear stability analysis techniques, the dependence of the non-stationary patterns on hyperbolicity is underlined at and close to the criticality. In particular, it is proven that inertial effects play a role, not only during transient regimes from the spatially-homogeneous steady state toward the patterned state but also in altering the amplitude, the wavelength, the migration speed, and even the stability of the travelling waves. Finally, in the last case, the formation and stability of stationary patterns are investigated in bi-dimensional domains. To this aim, a general class of two-species hyperbolic reaction-transport systems is deduced following the guidelines of Extended Thermodynamics theory. To characterize the emerging Turing patterns, linear and weakly nonlinear stability analysis on the uniform steady states are addressed for rhombic and hexagonal planform solutions. In order to gain some insight into the above-mentioned dynamics, the previous theoretical predictions are corroborated by numerical simulations carried out in the context of dryland ecology. In this context, patterns become a relevant tool to identify early warning signals toward desertification and to provide a measure of resilience of ecosystems under climate change. Such ecological implications are discussed in the context of the Klausmeier model, one of the easiest two-compartment (vegetation biomass and water) models able to describe the formation of patterns in semi-arid environments. Therefore, it will be also here discussed how the experimentally-observed inertia of vegetation affects the formation and stability of stationary and oscillatory periodic vegetation patterns.

Landscapes, as well as being physical spaces, are imagined and invested with meaning. The way they are thought about influences what is done to them. Conservation and development programmes in Zimbabwe's south-east 'lowveld' have been rooted in a particular conceptualisation of landscape - as wilderness. This derives from the experiences and priorities of colonial settlers and has had two facets. On the one hand the landscape came to be constituted as one of adventure, mystique and danger - a fearful place that 'pioneers' sought to tame into a productive landscape through cattle ranching or irrigation. On the other hand it has been viewed as a pristine natural landscape that must be preserved, rehabilitated or consciously manufactured. In both these manifestations African people were written out of the landscape. Their uses, perceptions and experiences of this landscape have been ignored in policies deriving from this 'wilderness vision'. Dryland agriculture in the low veld has been regularly dismissed as inappropriate, rather than a key livelihood strategy. Irrigation developments have been biased towards large-scale initiatives in the commercial sector. Livestock management strategies, other than those recommended for commercial ranching, have been discouraged. Wildlife utilisation schemes have delivered minimal returns to communities and imposed coercive regulations on resource use, deepening antagonism over land; but conservation initiatives such as a transfrontier national park are going ahead - bolstered by economic imperatives, global environmental agendas and donor priorities. Land reform has failed to take account of the way the landscape is bound up with identity through its embodiment of ancestral spirits and function as a repository of social memories. The turbulent dynamics around the ongoing farm invasions in Zimbabwe may open space for previously silenced constructions of landscape to influence policy. An awareness of the flexible and multiple nature of livelihood strategies and further debate on the restitution of ancestral lands would go a long way towards improving livelihoods in the lowveld.

Decomposition of organic matter is a critical component in global biogeochemical cycling. While decomposition rates have been robustly predicted for mesic systems, modeling decomposition dynamics in drylands has proven to be problematic, reflecting a need to account for processes that may be unique to dryland systems: low and spatially variable vegetation cover, high rates of soil movement, and high levels of radiant energy exposure at the soil surface. Recent empirical evidence suggests that the discrepancies between measured and predicted decomposition rates in drylands may be due to the greater influence of abiotic drivers, such as soil-litter mixing (SLM) and solar radiation, on plant litter decomposition relative to more mesic systems. UV-driven photodegradation may dominate until SLM reaches a threshold, at which point litter is shielded from radiation and microbial processes become predominant. The overarching goal of this dissertation was to examine the influence of SLM and solar radiation on decomposition of foliar and woody plant litter in a dryland ecosystem undergoing woody plant encroachment. A series of four complimentary experiments sought to quantify the effects of these abiotic drivers on decomposition in relation to variables such as vegetation patch type (e.g., beneath a shrub canopy, in a grass patch, on bare ground), radiant energy regime (e.g., full sun vs. shade), geomorphic surface (e.g., sandy, Holocene-age vs. clay-rich, Pleistocene-age soils), seasonality of litter fall (e.g., summer vs. winter), and litter quality (e.g., grass, shrub leaf, woody). Results indicate that interactions between SLM and photodegradation are complex and mediated by variations in ground cover which influence the local radiant energy environment and the movement of soil across the landscape by wind and water. Decomposition rates were significantly influenced by SLM, UV radiation, radiant energy regime, vegetation structure, and initial litter quality. While these results confirmed the importance of SLM and photodegradation as dryland decomposition drivers, they also reinforced the need for additional research to further clarify the relative importance of these processes under field conditions, particularly the interplay between UV radiation and SLM and their relative influence on biotic and abiotic decomposition processes. Given the changes in climate and vegetation projected for drylands, it is critical to further elucidate the influence of these processes on dryland biogeochemical cycling, as their effects may be magnified or dampened under future conditions. A deeper understanding of the processes driving biogeochemical cycling that may be unique to systems undergoing shifts in plant lifeform composition will allow us to better account for the fate of carbon in these globally important ecosystems.

Aquesta tesi avalua els efectes de diferents estratègies de fertilització amb purins de porc sobre la matèria orgànica del sòl (SOM) i les pèrdues de nitrogen associades a aquesta pràctica. El treball es va realitzar en parcel·les experimentals establertes l'any 2002 en condicions de secà (NE Espanya). L'origen del purí, la dosi i el moment d'aplicació van ser els principals factors avaluats. L'aplicació continuada de purins va augmentar la SOM, reduint l'aromaticitat de les substàncies húmiques analitzades. La matèria orgànica dels purins va desenvolupar en el sòl una repel·lència (superficial) a l'aigua (SWR) transitòria, que per a ser avaluada requereix adaptar els mètodes tradicionals de quantificació (amb aigua o amb solució d’etanol). A camp, la SWR no es va poder relacionar amb les emissions d'amoníac, que van variar entre 11% i el 18% del N amoniacal aplicat. El model LEACHM reprodueix de manera satisfactòria la dinàmica de l'aigua al sòl, tant en condicions de guaret com de conreu (ordi). El màxim d’aigua drenada per sota de 90cm de profunditat va ser de 14.3 mm/any. La dosi de purins (170 kg N/ha) recomanada per a zones vulnerables a la contaminació de nitrats també és recomanable per a reduir els impactes en el sistema aire-sòl-aigua en agricultura de secà.
Esta tesis evalúa los efectos de diferentes estrategias de fertilización con purín porcino sobre la materia orgánica del suelo (SOM) y las pérdidas de nitrógeno asociadas a esta práctica. La investigación se desarrolló a partir de parcelas experimentales de secano establecidas en el 2002 (NE de España), considerando como factores el origen del purín, la dosis y el momento de aplicación. La aplicación continuada de purines aumentó la SOM, reduciendo la aromaticidad de sustancias húmicas analizadas. La materia orgánica del purín aplicada desarrolló en el suelo (superficialmente) repelencia al agua (SWR) pero de efecto transitorio. Sin embargo, se requiere adaptar los métodos tradicionales de cuantificación (con agua o con una solución de etanol) para su evaluación. En campo, la SWR no pudo relacionarse con las emisiones de amoniaco, que variaron entre 11% y 18% del N amoniacal aplicado. El modelo LEACHM representó satisfactoriamente la dinámica del agua en el suelo en barbecho y bajo cultivo (cebada). El máximo drenaje, por debajo de 90 cm de profundidad, fue de 14.3 mm/año. La dosis de aplicación de purín (170 kgN/ha) autorizada en áreas vulnerables a la contaminación por nitratos también es recomendable para reducir los impactos en el sistema aire-suelo-agua en agricultura de secano.
This thesis evaluates the effects of different slurry fertilization strategies on the soil organic matter (SOM) and on the nitrogen-related losses outside the agricultural system. The work was performed in a long-term experimental field in a dryland system (NE Spain). Slurry origin, dose and application time were the main analysed factors. The slurry application increased the SOM reducing the aromaticity of the humic-like substances evaluated. The organic matter added with pig slurry developed superficial soil water repellency (SWR) but it was a transitory effect. Its quantification required to adapt the traditional methods of quantification (with water or with an ethanol solution). In the field, SWR could not be related to ammonia emissions, which ranged from 11% to 18% of the applied ammonium-N. The LEACHM model provided satisfactorily the soil water dynamics under fallow and in barley-growing seasons. The maximum annual water drainage was 14.3 mm below 90 cm depth. Slurry rate (170 kg-N/ha) allowed in nitrate vulnerable areas is also advisable to reduce negative slurry impacts in the air-soil-water system in dryland areas.

Adopting nitrogen (N)-fixing legumes into crop rotations is an accessible, ecological practice capable of increasing agricultural sustainability. Nonetheless, in northern Great Plains (NGP) wheat systems, proper water use management and the realization of N benefits are barriers to legumes replacing summer fallow. Legumes should also be able to mitigate legacies of soil organic matter losses from summer fallow. We conducted a participatory field-scale study in north-central Montana, assessing the viability of no-till, early-terminated legume green manures (LGMs) as summer fallow replacements. Soil water and nitrogen were measured to evaluate LGM effects on subsequent wheat crops. Farmers were interviewed to elucidate perspectives and challenges of adopting LGMs. Compared to fallow, LGMs depressed subsequent wheat yields by 6% (0.24 Mg ha -&#185;), and lowered grain protein at sites where wheat was fertilized with N (9 g kg -&#185;); grain protein was increased at unfertilized sites (5 g kg -&#185;). Absent rotational benefits from LGMs were attributed to dry conditions in the LGM year leading to low LGM biomass N and reduced N mineralization potential in soils, rather than soil water limitation to subsequent wheat. Farmers were curious about possible longterm benefits from LGMs, but expressed that the economic viability of LGMs appeared tenuous in the short-term. We also examined attributes and processes in soils from an eight-year-old rotation study containing fallow-wheat, continuous wheat, and legume-inclusive no-till rotations. We examined potentially mineralizable C and N (PMC and PMN), microbial biomass-C and wet aggregate stability (WAS). Nitrogen fertilizer was also added to a duplicate set of soils, and effects on C and N mineralization were evaluated. Legume-inclusive systems generally had higher levels of soil parameters, and had 26-50% greater PMN than wheat-only systems. Systems returning the most crop residue C to the soils had higher WAS regardless of legumes. Nitrogen additions depressed C and N mineralization. Results of these studies suggest that in NGP agroecosystems, LGMs can avoid limiting soil water available to subsequent wheat when terminated early and managed as no-till crops, but that legumes should be viewed as an investment in soil quality which may precipitate rotational N benefits more reliably after three or more appearances in rotation.

Water shortage is a serious threat for many societies worldwide. In drylands, water management measures like the construction of reservoirs are affected by eroded sediments transported in the rivers. Thus, the capability of assessing water and sediment fluxes at the river basin scale is of vital importance to support management decisions and policy making. This subject was addressed by the DFG-funded SESAM-project (Sediment Export from large Semi-Arid catchments: Measurements and Modelling). As a part of this project, this thesis focuses on (1) the development and implementation of an erosion module for a meso-scale catchment model, (2) the development of upscaling and generalization methods for the parameterization of such model, (3) the execution of measurements to obtain data required for the modelling and (4) the application of the model to different study areas and its evaluation. The research was carried out in two meso-scale dryland catchments in NE-Spain: Ribera Salada (200 km²) and Isábena (450 km²). Adressing objective 1, WASA-SED, a spatially semi-distributed model for water and sediment transport at the meso-scale was developed. The model simulates runoff and erosion processes at the hillslope scale, transport processes of suspended and bedload fluxes in the river reaches, and retention and remobilisation processes of sediments in reservoirs. This thesis introduces the model concept, presents current model applications and discusses its capabilities and limitations. Modelling at larger scales faces the dilemma of describing relevant processes while maintaining a manageable demand for input data and computation time. WASA-SED addresses this challenge by employing an innovative catena-based upscaling approach: the landscape is represented by characteristic toposequences. For deriving these toposequences with regard to multiple attributes (eg. topography, soils, vegetation) the LUMP-algorithm (Landscape Unit Mapping Program) was developed and related to objective 2. It incorporates an algorithm to retrieve representative catenas and their attributes, based on a Digital Elevation Model and supplemental spatial data. These catenas are classified to provide the discretization for the WASA-SED model. For objective 3, water and sediment fluxes were monitored at the catchment outlet of the Isábena and some of its sub-catchments. For sediment yield estimation, the intermittent measurements of suspended sediment concentration (SSC) had to be interpolated. This thesis presents a comparison of traditional sediment rating curves (SRCs), generalized linear models (GLMs) and non-parametric regression using Random Forests (RF) and Quantile Regression Forests (QRF). The observed SSCs are highly variable and range over six orders of magnitude. For these data, traditional SRCs performed poorly, as did GLMs, despite including other relevant process variables (e.g. rainfall intensities, discharge characteristics). RF and QRF proved to be very robust and performed favourably for reproducing sediment dynamics. QRF additionally excels in providing estimates on the accuracy of the predictions. Subsequent analysis showed that most of the sediment was exported during intense storms of late summer. Later floods yielded successively less sediment. Comparing sediment generation to yield at the outlet suggested considerable storage effects within the river channel. Addressing objective 4, the WASA-SED model was parameterized for the two study areas in NE Spain and applied with different foci. For Ribera Salada, the uncalibrated model yielded reasonable results for runoff and sediment. It provided quantitative measures of the change in runoff and sediment yield for different land-uses. Additional land management scenarios were presented and compared to impacts caused by climate change projections. In contrast, the application for the Isábena focussed on exploring the full potential of the model's predictive capabilities. The calibrated model achieved an acceptable performance for the validation period in terms of water and sediment fluxes. The inadequate representation of the lower sub-catchments inflicted considerable reductions on model performance, while results for the headwater catchments showed good agreement despite stark contrasts in sediment yield. In summary, the application of WASA-SED to three catchments proved the model framework to be a practicable multi-scale approach. It successfully links the hillslope to the catchment scale and integrates the three components hillslope, river and reservoir in one model. Thus, it provides a feasible approach for tackling issues of water and sediment yield at the meso-scale. The crucial role of processes like transmission losses and sediment storage in the river has been identified. Further advances can be expected when the representation of connectivity of water and sediment fluxes (intra-hillslope, hillslope-river, intra-river) is refined and input data improves.
In vielen Regionen der Erde stellt Wassermangel ein Problem für die menschliche Gesellschaft dar. Insbesondere in Trockengebieten werden jedoch Maßnahmen des Wassermanagements, wie die Wasserspeicherung in Stauseen, durch die im Fluss transportierten Sedimentfrachten negativ beeinflusst. Somit stellen eine adäquate Beurteilung von Wasser- und Sedimentflüssen eine wichtige Voraussetzung für Entscheidungen in Wassermanagement und -planung dar. Dieser Problematik widmete sich das SESAM-Projekt (Sediment Export from large Semi-Arid catchments: Measurements and Modelling). Im Rahmen dieses Projektes befasste sich diese Dissertation mit (1) der Entwicklung und Umsetzung eines Erosions-Moduls für ein Einzugsgebietsmodell auf der Meso-Skala, (2) der Entwicklung von Skalierungs- und Generalisierungsmethoden für die Parametrisierung eines solchen Modells, (3) der Durchführung von Messungen, um die notwendigen Daten für das Modell zu gewinnen und (4) die Anwendung des Modells für verschiedene Einzugsgebiete und seiner Bewertung. Die Studie umfasste zwei mesoskalige Trockeneinzugsgebiete in NO-Spanien: Ribera Salada (200 km²) und Isábena (450 km²). Im Hinblick auf Zielstellung 1 wurde WASA-SED, ein räumlich semi-distribuiertes Modell für Wasserflüsse und Sedimenttransport, entwickelt. Das Modell simuliert Abfluss- und Erosionsprozesse auf der Hangskala, den Transport von suspendierten und Geschiebesedimenten auf der Skala von Flussabschnitten sowie Rückhalt- und Remobilisierungsprozesse von Sedimenten in Stauseen. Die vorliegende Arbeit stellt das Modellkonzept und Modellanwendungen vor und beschreibt Fähigkeiten und Grenzen des Modells. Die Modellierung auf größeren Skalen beinhaltet das Dilemma, dass relevante Prozesse beschrieben werden müssen, gleichzeitig aber die Anforderungen an Eingabedaten und Rechenzeit realisierbar bleiben. In WASA-SED wird diesem durch die Anwendung eines innovativen Hangprofil-basierten Skalierungsansatzes Rechnung getragen, indem die Landschaft durch charakteristische Toposequenzen repräsentiert wird. Um derartige Toposequenzen hinsichtlich verschiedener Landschaftseigenschaften (z.B. Relief, Böden, Vegetation) abzuleiten, wurde in Bezug zur Zielstellung 2 der LUMP-Algorithmus (Landscape Unit Mapping Program) entwickelt. LUMP beinhaltet ein Verfahren zur Berechnung repräsentativer Hangprofile und ihrer Attribute aus einem digitalen Geländemodell und optionalen Zusatzdaten. Durch die Klassifikation dieser Hangprofile wird die Grundlage der räumlichen Diskretisierung des WASA-SED Modells bereitgestellt. Im Zusammenhang mit Zielstellung 3 wurden Abfluss und Sedimentkonzentration (SSC) am Auslass und in einigen Teileinzugsgebieten des Isábena-Einzugsgebietes gemessen. Um den Sedimentaustrag zu bestimmen, mussten die Einzelmessung der Sedimentkonzentration interpoliert werden. Diese Arbeit vergleicht die Eignung traditioneller Eichkurvenansätze (SRCs), Generalized Linear Models (GLMs) und der nichtparametrischen Regressionstechniken Random Forests (RF) und Quantile Regression Forests (QRF). Da die beobachteten SSC-Werte stark über sechs Größenordnungen variieren, erwiesen sich die traditionellen SRCs als unzureichend. Gleichfalls versagten GLMs trotz der Einbeziehung weiterer relevanter Prozessgrößen wie Niederschlagsintensitäten und Abflusscharakteristika. RF und QRF stellten sich hingegen als sehr robust und für die Rekonstruktion der Sedimentdynamik geeignet dar. QRF liefert darüber hinaus auch Informationen zur Genauigkeit dieser Schätzungen. Die darauf aufbauende Analyse ergab, dass der Großteil der Sedimentfracht während der Starkregenereignisse des Spätsommers transportiert wurde. Spätere Niederschlagsereignisse erzeugten deutlich geringeren Austrag. Durch den Vergleich von Sedimentfrachten im Oberlauf mit Austragsmengen am Gebietsauslass konnte die Bedeutung der Sedimentspeicherung im Flussbett identifiziert werden. Zielstellung 4 wurde bearbeitet, indem das WASA-SED-Modell für zwei Untersuchungsgebiete in NO-Spanien unter unterschiedlichen Gesichtspunkten angewendet wurde. Für das Ribera-Salada-Einzugsgebiet lieferte das unkalibrierte Modell plausible Ergebnisse hinsichtlich der Wasser- und Sedimentflüsse. Damit war es möglich, die potentiellen Änderungen dieser Größen durch verschiedene Landnutzungsszenarien zu quantifizieren. Diese wurden den prognostizierten Veränderungen, die durch Klimaänderungen hervorgerufen würden, gegenübergestellt. Im Gegensatz dazu konzentrierte sich die Anwendung im Isábena-Einzugsgebiet auf die Untersuchung der bestmöglichen Modellanpassung. Im Validierungszeitraum ergab sich eine befriedigende Modellgüte für Wasser- und Sedimentflüsse. Diese Gesamtgüte wurde maßgeblich durch die unzureichende Abbildung der Unterliegergebiete beeinflusst, wohingegen die Gebiete des Oberlaufs, trotz ihrer stark kontrastierenden Sedimentausträge, gut dargestellt wurden. Die Anwendung des WASA-SED-Modells auf drei verschiedene Untersuchungsgebiete bestätigt die generelle Eignung des Modellkonzepts als einen sinnvollen multiskaligen Ansatz, der in einem Modell effektiv die Hangskala mit der Einzugsgebietsskala sowie den Einfluss von Flüssen und Stauseen vereint. Er stellt somit eine mögliche Grundlage für die Bearbeitung von wasser- und sedimentbezogenen Fragestellungen auf der Meso-Skala dar. Die besondere Bedeutung der Prozesse der Sickerverluste und Sedimentspeicherung im Gerinne konnten herausgearbeitet werden. Mögliche Verbesserungen betreffen die Berücksichtigung der Konnektivität von Wasser- und Sedimentflüssen (auf dem Hang, zwischen Hang und Fluss, innerhalb des Flusses) und die Qualität der Eingangsdaten für das Modell.

Dryland ecosystems contain small amounts of Carbon (C), yet very little information is available about C dynamics in dryland soils. Cyanobacterial soil crusts are considered a major source of organic C in drylands through photosynthesis. Through photosynthesis, cyanobacteria produce extracellular polysaccharides (EPS) increasing soil organic C (SOC) pool as carbohydrates.

Drylands are characterised by patchy vegetation, erodible surfaces and erosive aeolian processes. The extreme nature of dryland environments means that semi-arid vegetation cover is often dynamic through time and space, due to complex relationships among plants, soil and transport processes. Understanding how ecogeomorphic processes interact and shape landscape evolution is critical for managing potential environmental and anthropogenic impacts in drylands, since these vulnerable regions are often used for pastoralism, agriculture and habitation. Despite a wealth of vegetation distribution models that simulate distinctive patterning that is often observed in drylands, relatively little is known about the effects of vegetation patch distribution, geometry and scale on the entrainment and transport of aeolian sediment. Empirical and modelling studies have shown that vegetation elements provide drag on the overlying airflow, thus affecting wind velocity profiles and altering erosive dynamics on desert surfaces. However, these dynamics are significantly complicated by turbulence, porosity and pliability effects in canopies. This thesis therefore presents new high-resolution field data for parameterising wind flow around individual plants and vegetation patches. Wind transport models have played a key role in simplifying aeolian processes in partly vegetated landscapes, but they remain challenging in some respects. Most models do not recognise the heterogeneous nature of desert surfaces, and those that do are often computationally expensive to run. Cellular automaton (CA) modelling has been successfully used to simulate dryland ecogeomorphic processes over large spatial and temporal scales. However, no existing CA model explicitly links vegetation growth, wind flow dynamics and sediment flux over a surface. This thesis presents a new CA approach that couples a sophisticated vegetation distribution model with a sediment transport model. The Vegetation and Sediment TrAnsport model (ViSTA) is verified and validated against existing dunefield theory and field datasets. ViSTA is then forced with potential 21^st century climate and land use change scenarios, to characterise possible transition scenarios between environmental states in the Kalahari Desert. ViSTA is shown to be a robust geomorphological tool for predicting landscape responses to a variety of human and environmental stresses.

Little research has been done in the humid mid-Atlantic region to develop full-season N fertilizer recommendations for dryland no-tillage grain sorghum (Sorghum bicolor L. Moench) production. The objectives of this study were: (i) to determine the optimum rate of band-placed starter N fertilizer needed in combination with side-dress N applications to achieve economic grain yields, (ii) to investigate if pre-plant broadcast N applications are as efficient as band-placed plus side-dress N applications, (iii) to evaluate the response of grain sorghum yield to partitioned side-dress N applications, and (iv) to study the influence of residual soil profile mineral-N (nitrate and ammonium) on sorghum response to applied N fertilization. Multi-location field studies were conducted over three years. A range of N treatments of various starter-band and side-dress N rates were applied. The experimental data indicate that an optimum rate of N fertilization depends on residual soil mineral-N. Little or zero starter-band-N in conjunction with side-dress-N applications of 130 kg of N ha-1 for soils testing high in mineral-N ( 50 kg N ha-1 in the top 0.3m of surface soil) at planting, and a starter-band-N supplement of 40 kg N ha-1 in conjunction with 130 kg N ha-1 side-dress N for soils testing low in mineral-N at planting, optimized the grain sorghum yields in these experiments. Broadcast N applications were observed to be as efficient as band placed N applications when followed by rainfall soon after application. Grain sorghum yields did respond to the partitioned side-dress N applications. However, partitioning of side-dress N application again depends on the residual mineral-N level present in the soil. In order to consider residual soil mineral-N in making N fertilizer recommendations "Associated Nitrogen Fertilizer Equivalency" (ANFE) values were calculated. ANFE is the amount of applied N that has potential to produce the same yield as that produced by the residual soil mineral-N. The N fertilizer recommendations based on ANFE values were quite close for two out of four sites as compared to the N rates at which the maximum yields were obtained in this study.
Ph. D.

Landholders in the Booberoi to Quandialla (B-Q) Transect area, located in central west NSW, have been concerned about an emerging dryland salinity problem since the late 1990�s (Wooldridge 2002, pers. comm. Muller 2002, pers. comm.) with borehole information and electromagnetic induction investigations supporting anecdotal observations. The presence of indicator vegetation, waterlogging of soils and salinisation of land are becoming increasingly prevalent, with two well-documented sites including �Strathairlie� near Quandialla, and �Back Creek� near West Wyalong. The B-Q Transect area lies within the Bland Creek Catchment, a broad open plain of subdued topography and restricted drainage receiving sediments from elevated rises located to the west, south and east. Significant deposits of transported alluvial materials have in-filled the catchment to depths in excess of 160 m and have posed a particular impediment to regional-scale mineral exploration. Stream flow across the alluvial plains and low angle alluvial fans is intermittent with most of the flow being diverted into groundwater storage or lost to evaporation. Rarely do streams flow into Lake Cowal to the north. A partial electromagnetic (EM) induction survey coupled with a long term bore and piezometer network monitoring program have been implemented by the Department of Infrastructure, Planning and Natural Resources (DIPNR � formerly Department of Land and Water Conservation) Central West NSW Salt Group. These programs allow for initial, broad-scale evaluation of the magnitude and spatial distribution of the salinity problem but fail to pinpoint remaining sites at risk as well as the mechanisms of salt emplacement. As part of an approach to assist with hazard mitigation and land management, two regolith-landform maps are being compiled using 1:20,000 scales in the Back Creek and Quandialla areas. A third, more regional regolith-landform map at 1:50,000 scale (Holzapfel & Moore 2003a, b & c) provides context for the more detailed mapping areas. The new regolith-landform maps will aid in interpretation of existing geophysical techniques, help piece together the three-dimensional characteristics of the Bland Creek catchment, aid in the development of a shallow fluid flow and palaeotopographic model and assist land managers in formulating land management units (LMU�s). The three-dimensional integration of regolith-landform mapping, electromagnetic studies, bore information and other geophysical methods is critical in determining the interaction, distribution and movement of groundwater in the Bland Creek Catchment as buried palaeochannels represent preferred fluid pathways. The distribution of these palaeochannels has implications for future dryland salinity outbreaks, the remediation of current outbreaks and mineral exploration closer to the well-known Wyalong Goldfield (Lawrie et al., 1999). The western quarter of the B-Q Transect area partially overlaps with the recently completed GILMORE Project (Lawrie et al., 2003a,b & c), a multi-disciplinary study, coordinated by Geoscience Australia (GA) and the Bureau of Rural Sciences (BRS). Regolith-landform information in addition to gamma-ray spectrometry, magnetics, airborne electromagnetics and a digital elevation model acquired by the GILMORE Project have been incorporated into regolith-landform maps over the B-Q Transect. The incorporation of these datasets has helped not only extend the usefulness of the GILMORE Project data but provide a consistent, regolith-landform coverage for the broader Bland Creek Catchment. Regolith-landform mapping has been successful in highlighting major recharge zones for local and intermediate flow systems. The mechanisms for dryland salinity at two well-known sites have also been determined. Increasing salt stores are occurring through evaporation of intermittent floodwaters sourced from floodplains, back plains and broad meandering existing creek systems and recharging partially exposed palaeochannels intersecting the surface. Due to the shallow nature of these partially exposed palaeochannels, evaporation further concentrates the salt load in the soil profile. It is unknown if mapped shallow palaeochannels further away from current drainage systems are affected by rising salt loads. Regolith-landform mapping highlights two additional risk factors common to the 1:50,000 and 1:20,000 scale B-Q Transect mapping areas including widespread waterlogging of soils and wind erosion. Due to the subdued topography, features such as gilgai, fences and roads are having an effect on drainage modification. Wind erosion was also observed to play a major role within the B-Q Transect with significant loss of topsoil creating hardened clay surfaces resistant to water infiltration and significant redistributed deposits of aeolian materials. Interpretation of regolith-landform mapping against geophysical datasets and drill hole data show considerable lateral and vertical variation of regolith units. This variation of regolith distribution with depth does not reduce the effectiveness of using regolithlandform mapping as a valued management tool. The subdued relief coupled with the complex interplay between recharge zones, discharge zones and surficial drainage networks over the B-Q Transect still requires a detailed knowledge of surface regolithlandform characteristics whilst reinforcing the need for a multidisciplinary approach to gain a 3D perspective. Catchment analysis has been performed on drainage systems within the Bland Creek Catchment and has helped explain the strong effect different catchments have had on sediment supply to the Bland Basin. Catchment analysis results have been used in basic calculations of salt loads in the Bland Creek Catchment. An estimated 18,780 Tonnes/yr of salt enter the Bland Creek catchment and as stream flow out of the Bland Creek Catchment is intermittent, salt stores are increasing in the upper margins of the soil profile and groundwater reserves. Reconstruction of the palaeotopography of the B-Q Transect has been made possible using a mutli-disciplinary approach incorporating information from regolith-landform mapping, drill hole information, gamma-ray spectrometry and GILMORE Project datasets. The production of large-scale regolith-landform mapping, the development of a shallow fluid flow model and reconstruction of palaeotopography builds on and contributes to knowledge of the Bland Creek Catchment allowing for detailed farmscale and paddock-scale land management decisions.

Many aspects concerning the association of riverine fish with in-channel habitat remain poorly understood, greatly hindering the ability of researchers and managers to address declines in fish assemblages. Recent insights gained from landscape ecology suggest that small, uni-scalar approaches are unlikely to effectively determine those factors that influence riverine structure and function and mediate fish-habitat associations. There appears to be merit in using multiple-scale designs built upon a geomorphologically-derived hierarchy to bridge small, intermediate and large spatial scales in large rivers. This thesis employs a hierarchical design encompassing functional process zones (referred to hereafter as zones), reaches and mesohabitats to investigate fish-habitat associations as well as explore patterns of in-channel habitat structure in one of Australia's largest dryland river systems; the Barwon-Darling River. In this thesis, empirical evidence is presented showing that large dryland rivers are inherently complex in structure and different facets of existing conceptual models of landscape ecology must be refined when applied to these systems. In-channel habitat and fish exist within a hierarchical arrangement of spatial scales in the riverscape, displaying properties of discontinuities, longitudinal patterns and patch mosaics. During low flows that predominate for the majority of time in the Barwon-Darling River there is a significant difference in fish assemblage composition among mesohabitats. There is a strong association between large wood and golden perch, Murray cod and carp, but only a weak association with bony herring. Golden perch and Murray cod are large wood specialists, whereas carp are more general in there use of mesohabitats. Bony herring are strongly associated with smooth and irregular banks but are ubiquitous in most mesohabitats. Open water (mid-channel and deep pool) mesohabitats are characterised by relatively low abundances of all species and a particularly weak association with golden perch, Murray cod and carp. Murray cod are weakly associated with matted bank, whereas carp and bony herring associate with this mesohabitat patch in low abundance. Nocturnal sampling provided useful information on size-related use of habitat that was not evident from day sampling. Both bony herring and carp exhibited a variety of habitat use patterns throughout the die1 period and throughout their lifetime, with temporal partitioning of habitat use by juvenile bony herring and carp evident. Much of the strong association between bony herring and smooth and irregular banks was due to the abundance of juveniles (<100mm in length) in these mesohabitats. Adult bony herring (>100mm length) occupied large wood more than smooth and irregular banks. At night, juvenile bony herring were not captured, suggesting the use of deeper water habitats. Adult bony herring were captured at night and occupjed large wood, smooth bank and irregular bank. Juvenile carp (<200mm length) were more abundant at night and aggregated in smooth and irregular banks more than any other mesohabitat patch. Adult carp (>200mm length) occupied large wood during both day and night. There is a downstream pattern of change in the fish assemblage among river zones, with reaches in Zone 2 containing a larger proportion of introduced species (carp and goldfish) because of a significantly lower abundance of native species (bony herring, golden perch and Murray cod) than all other zones. In comparison, the fish assemblage of Zone 3 was characterised by a comparatively higher abundance of the native species bony herring, golden perch and Murray cod. A significant proportion of the amongreach variability in fish assemblage composition was explained at the zone scale, suggesting that geomorphological influences may impose some degree of top-down constraint over fish assemblage distribution. Although mesohabitat composition among reaches in the Barwon-Darling River also changed throughout the study area, this pattern explained very little of the large-scale distribution of the fish assemblage, with most of the variability in assemblage distribution remaining unexplained. Therefore, although mesohabitat patches strongly influence the distribution of species within reaches, they explain very little of assemblage composition at intermediate zone and larger river scales. These findings suggest that small scale mesohabitat rehabilitation projects within reaches are unlikely to produce measurable benefits for the fish assemblage over intermediate and large spatial scales in the Barwon-Darling River. This indicates the importance taking a holistic approach to river rehabilitation that correctly identifies and targets limiting processes at the correct scales. The variable nature of flow-pulse dynamics in the Barwon-Darling River creates a shifting habitat mosaic that serves to maintain an ever-changing arrangement of habitat patches. The inundation dynamics of large wood habitat described in this thesis highlights the fragmented nature of mesohabitat patches, with the largest proportion of total in-channel large wood remaining unavailable to fish for the majority of the time. At low flows there is a mosaic of large wood habitat and with increasing discharge more potential large wood habitat becomes available and does so in a complex spatial manner. What results in this dryland river is a dynamic pattern of spatio-temporal patchiness in large wood habitat availability that is seen both longitudinally among different river zones and vertically among different heights in the river channel. Water resource development impacts on this shifting habitat mosaic. Projects undertaking both fish habitat assessment and rehabilitation need to carefully consider spatial scale since the drivers of fish assemblage structure can occur at scales well beyond that of the reach. Fish-habitat associations occurring at small spatial scales can become decoupled by process occurring across large spatial scales, making responses in the fish assemblage hard to predict. As rivers become increasingly channelised, there is an urgent need to apply research such as that conducted in this thesis to better understand the role that in-channel habitats play in supporting fish and other ecosystem processes. Habitat rehabilitation projects need to be refined to consider the appropriate scales at which fish assemblages associate with habitat. Failure to do so risks wasting resources and forgoes valuable opportunities for addressing declines in native fish populations. Adopting multi-scalar approaches to understanding ecological processes in aquatic ecosystems, as developed in this thesis, should be a priority of research and management. To do so will enable more effective determination of those factors that influence riverine structure and function at the approariate scale.

Bibliography: leaves 72-81.
Dryland degradation is widely viewed as a major environmental issue and in many parts of Namibia is perceived to be significant to severe. In recent years, however, following a worldwide trend, there has been a re-evaluation and questioning of the extent, nature and causes of dryland degradation. Too often it seems pronouncements of degradation are based on limited data and a poor understanding of the context and functioning of dryland ecosystems. The aim of this report, therefore, is to demonstrate why an historical perspective of environmental dynamics is valuable in drylands for the identification of degradation and to evaluate the use of such a perspective using northern Damaraland a case study. In order to achieve this aim, several objectives were addressed, these being: to provide a clear and unambiguous definition of the term 'dryland degradation' or 'land degradation'; to review possible indicators and agents of environmental change and land degradation; to provide a conceptual framework that emphasises the importance of an historical; perspective, and the role of arid rangeland dynamics, in evaluating environmental change; to analyse environmental dynamics in northern Damaraland from an historical perspective, utilising aerial photography and archival data in the form of stock numbers; to highlight inherent problems and the utility of an historical perspective.

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第22163号
農博第2377号
新制||農||1074(附属図書館)
学位論文||R2||N5243(農学部図書室)
京都大学大学院農学研究科地域環境科学専攻
(主査)教授 舟川 晋也, 教授 縄田 栄治, 准教授 真常 仁志
学位規則第4条第1項該当

The reported requirement for a higher weeding effort due to increased weed infestations under conservation agriculture (CA) relative to conventional mouldboard plough tillage is perceived by both smallholder farmers and extension workers as the main limiting factor to the widespread adoption of CA by smallholder farmers in southern Africa. However, proponents of CA argue that weeds are only a problem under CA in the initial two years and decline afterwards resulting in reduced labour requirements for weeding under CA. They further posit that weeds are only major problem where minimum tillage (MT) is adopted without crop residue mulching and diverse crop rotations. This thesis explores the effect of time under CA on weed population dynamics and crop growth under the recommended CA practices and actual smallholder farmer practice in semi-arid Zimbabwe. Assessment of weed and crop growth on a long-term CA experiment at Matopos Research Station revealed that the MT systems of planting basins and ripper tine were associated with higher early season weed density and biomass than conventional early summer mouldboard tillage (CONV) in both the fifth (cowpea phase) and sixth (sorghum phase) years of CA. This increased weed infestation within the first four weeks after planting in CA necessitated early weeding to provide a clean seedbed and avert significant crop yield loss. Maize mulching only suppressed early season weed growth in sorghum mostly at a mulch rate of 8 t ha-1 which is not a mulching rate that is attainable on most smallholder farms. However, the lower maize residue mulch rate of 4 t ha-1 was consistently associated with increased weed emergence and growth as from the middle of the cropping season in both crop species. The increased weed infestations under the mulch were probably due to the creation of ‘safe sites’ with moist conditions and moderate temperatures. The high weed growth under the mulch contributed to the low sorghum grain yield obtained under mulched plots. In addition, maize mulching was also associated with a less diverse weed community that was dominated by the competitive Setaria spp. and difficult to hoe weed Eleusine indica (L.) Gaertn. However, the weed community under CA was similar to that under CONV tillage with no evidence of a shift to the more difficult to control weed species. The increased early season weed growth and high weed pressure under CA meant that it was still necessary to hoe weed four times within the cropping season to reduce weed infestations and improve crop growth even after four years of recommended CA practices. Early and frequent weeding was effective in reducing weed growth of most species including Setaria spp. and E. indica demonstrating that on smallholder farms where labour is available hoe weeding can provide adequate weed control. The wider spacing recommended for use in CA contributed to the low cowpea and sorghum grain yields obtained under CA compared to CONV tillage. On smallholder farms in Masvingo District, the MT system of planting basin (PB) was the only conservation farming (CF) component adopted by farmers. There was no difference in the total seedling density of the soil weed seed bank and density of emerged weeds in the field in PB and conventional mouldboard ploughing done at first effective rains (CONV tillage). However, the first weeding in PB was done at least 15 days earlier (P < 0.05) than in CONV tillage suggesting high early season weed growth in PB relative to CONV tillage. As weed density did not decline with time in PB, weed management did not differ with increase in years under PB. Shortage of inputs such as seed and fertiliser was identified by smallholder farmers as the most limiting factor in PB crop production with the area under PB was equivalent to the seed and fertiliser provided by CARE International for most farmers. On this small area, weeds could be managed by available family labour. Double the maize grain yield was obtained in PB (mean: 2856 kg ha-1) due to improved weed management and soil fertility. However, the use of poorly stored composts was found to introduce weeds into some PB fields. The findings of this study demonstrated that weed pressure was still high and weed management were still a challenge under the practice recommended to smallholder farmers in Zimbabwe even in the sixth year of practice. There is, therefore, a need for research on the economic feasibility of using herbicides, intercropping and optimal crop density to ameliorate the high weed pressure under CA.
Thesis (PhD)--University of Pretoria, 2013.
Plant Production and Soil Science
unrestricted