An imperative of the South African government is to increase agricultural production in rural areas. In support of this, a project was initiated in the Mlondozi district of Mpumalanga Province under the National LandCare programme. The goal was to assess land management practices contributing to sustainable and profitable agricultural production. Medium-term liming experiments were sampled to a range of lime treatments in a Hutton and Oakleaf soil. Critical thresholds where a reduction in relative grain yield was found were at a pH (H2O), extractable acidity, Al and acid saturation of 5.49, 0.277 cmolc kg soil-1, 0.145 cmolc kg soil-1 and 13%, respectively. Critical soil fertility threshold levels were established at 50 mg K kg-1, 228-345 mg Ca kg-1, 78-105 mg Mg kg-1 and 1.68-2.83 mg Cu kg-1. Nutrient vector analysis showed a toxic build-up of Fe, followed by Al and to a lesser extent Mn, which depressed the uptake of Ca, Mg and B in the Hutton soil. In the Oakleaf soil, Al toxicity, followed by high concentrations of Mn and Fe, markedly reduced the uptake of Ca, Mg and K by maize. Net rates of acid production in the soil profile varied between 1.61 and 2.44 kmol H+ ha-1 year-1 for the Hutton soil and between 4.59 and 8.82 kmol H+ ha-1 year-1 in the Oakleaf soil due to liming. A decline of 0.046 pH unit year-1 for an initial pH(H2O) value of 5.33, and 0.140 pH unit year-1 for an intial pH(H2O) of 6.47, respectively, in the Hutton was recorded. For the Oakleaf these declines were 0.044 and 0.110 pH unit year-1, from pH(H2O) 4.54 and 5.15. Maintenance liming amounts at different pH values for the Hutton soil were equivalent to 0.2, 0.3 and 1.4 tonnes CaCO3 ha-1 annually, while 0, 0.8 and 0.8 tonne CaCO3 ha-1 annually were recorded for the Oakleaf soil. The study was extended to 80 random topsoil samples in the district. Relationships of soil BC over limited pH ranges showed that at soil BC (pH<4.5) the main buffering mechanism was extractable Al > organic C > clay. At soil BC (pH4.5-6.5) the buffering mechanism was extractable Al > clay > CBD-Al > organic C > CBD-Fe. The main buffering mechanism between pH 6.5-8.5 was clay > CBD-Fe, organic C > CBD-Al. Acid production for 30 crop production sites varied from a measured 0.21 to 10.31 (mean 3.70) kmol H+ ha-1 year-1 The rate of pH decline for the top 0-250 mm depth was between 0.051 and 0.918 (mean 0.237) pH units year-1. In the absence of remedial lime applications, pH (H2O) values in most of the area are projected to decrease to the critical value of 5.68 or lower within 4 years. Soil with a pH (H2O) value of >5.73, extractable Al and acidity of <0.18 and <0.25 cmolc kg-1 soil, respectively, clay content of ≤26%, and a ECEC value of ≤3.29 cmolc kg soil-1, are at greater risk of acidification as gradual acceleration in soil acidification takes place at the above-mentioned critical thresholds. / Thesis (PhD)--University of Pretoria, 2010. / Plant Production and Soil Science / unrestricted

Increasing urbanization is often accompanied by problematic changes in watershed hydrology. Decreasing surface permeability can lead to increased overland flow volumes, which may spread surficial contaminants and increase the strain on municipal stormwater infrastructure. This study examines a mixed-use property in the Proctor Creek watershed in Atlanta, Georgia, to better understand how land-management practices influence soil overland flow potential. Field saturated hydraulic conductivity (Kfs) measurements were collected from soils 1) subjected to compaction, 2) in urban agricultural use, and 3) under common lawn maintenance. Mean values were 9.1E-7 cm/s, 2.2E-4 cm/s, and 9.0E-6 cm/s respectively. Measurements were collected in-situ with the use of the Aardvark constant-head permeameter. Statistical analyses indicated a substantial difference in Kfs based on land-management practices and that urban farming can increase soil Kfs and limit overland flow. Additional analysis revealed no significant difference in grain-size distributions suggesting land-management practices controlled Kfs, not soil texture.

Thesis (M.Sc. (Geography)) --University of Limpopo, 2018 / Soil erosion, which is a critical component of land degradation, is one of the serious global environmental problems often threatening food security, water resources, and biodiversity. A comprehensive assessment and analysis of remote sensing applications in the spatial soil erosion mapping and monitoring over time and space is therefore, important for providing effective management and rehabilitation approaches at local, national and regional scales. The overall aim of the study was to assess the use of multispectral remote sensing sensors in mapping and monitoring the spatio-temporal variations in levels of soil erosion in the former homelands of Sekhukhune district, South Africa. Firstly, the effectiveness of the new and freely available moderate-resolution multispectral remote sensing data (Landsat 8 Operation Land Imager: OLI and Sentinel-2 Multi-Spectral Instrument: MSI) derived spectral bands, vegetation indices, and a combination of spectral bands and vegetation indices in mapping the spatio-temporal variation of soil erosion in the former homelands of Sekhukhune District, South Africa is compared. The study further determines the most optimal individual sensor variables that can accurately map soil erosion. The results showed that the integration of spectral bands and spectral vegetation indices yielded high soil erosion overall classification accuracies for both sensors. Sentinel-2 data produced an OA of 83, 81% whereas Landsat 8 has an OA of 82.86%. The study further established that Sentinel-2 MSI bands located in the NIR (0.785-0.900 μm), red edge (0.698-0.785μm) and SWIR (1.565-2.280 μm) regions were the most optimal for discriminating degraded soils from other land cover types. For Landsat 8 OLI, only the SWIR (1.560-2.300 μm), NIR (0.845-0.885 μm) region were selected as the best regions. Of the eighteen spectral vegetation indices computed, Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI) and Global Environmental Monitoring Index (GEMI) were selected as the most suitable for detecting and mapping soil erosion. Secondly, the study assessed soil erosion in the former homelands of Sekhukhune, South Africa by applying a time-series analysis (2002 and 2017), to track changes of areas affected by varying degrees of erosion. Specifically, the study assessed and mapped changes of eroded areas (wet and dry season), using multi-date Landsat products 8 OLI and 7 Enhanced Thematic Mapper (ETM+)). Additionally, the study used extracted eroded areas and overlay analysis was performed together with geology, slope and the Topographic Wetness Index (TWI) of the area under study to assess whether and to what extent the observed erosional trends can be explained. ii Time series analysis indicated that the dry season of 2002, experienced 16.61 % (224733 ha) of erosion whereas in 2017 19.71% was observed. A similar trend was also observed in the wet season. This work also indicates that the dominant geology type Lebowa granite: and Rustenburg layered its lithology strata experienced more erosional disturbances than other geological types. Slopes between 2-5% (Nearly level) experienced more erosion and vice-versa. On the hand, the relationship between TWI and eroded areas showed that much erosion occurred between 3 and 6 TWI values in all the seasons for the two different years, however, the dry season of 2002 had a slightly higher relationship and vice-versa. We, therefore, recommend use and integration of freely and readily available new and free generation broadband sensors, such as Landsat data and environmental variables if soil erosion has to be well documented for purposes of effective soil rehabilitation and conservation. Keywords: Food security Global changes, Land degradation, Land-based ecosystems, Land management practices, Satellite data, Soil conservation, Sustainable Development; Topographic Wetness Index; Time series analysis.

Die Landwirtschaft liefert einen Großteil der Nahrungsmittel und Rohstoffe für den menschlichen Verbrauch und wird aufgrund globaler Dynamiken des Bevölkerungswachstums, Änderungen der Ernährungszusammensetzung und Auswirkungen des Klimawandels herausgefordert. Gleichzeitig hat die intensive landwirtschaftliche Produktion oft erhebliche Auswirkungen auf die Leistungen und Funktionen von Ökosystemen. Agrarökosystemmodelle können verwendet werden, um Auswirkungen der Landwirtschaft über verschiedene zeitliche und räumliche Skalen zu quantifizieren. Globale Bewertungen werden jedoch durch die begrenzte Verfügbarkeit von Daten einzelner agronomischer Maßnahmen und dem Wissen über die damit verbundenen biophysikalischen und biogeochemischen Prozesse erschwert. Ziel dieser Doktorarbeit ist es, das Verständnis über Anforderungen an Daten von landwirtschaftlichen Produktionssystemen und deren Anwendungsmethoden in globalen Modellierungsstudien zu erweitern. Darüber hinaus zielt diese Doktorarbeit darauf ab die Arten, räumliche Ausdehnung, Umweltwirkung und Potenziale von unterschiedlichen Bewirtschaftungsmethoden auf globalem Ackerland abzuschätzen. Die Ergebnisse der ersten Studie zeigen, inwiefern die Aggregation von rasterzellenbasiert simulierten Ernteerträgen zu national und globalen Durchschnittserträgen mit vier unterschiedlichen Datenprodukten zu Unsicherheiten von ~10 % führen kann. Der zweite Forschungsartikel präsentiert eine Klassifikation von sechs Bodenbearbeitungssystemen, deren Kartierung und ermittelten Merkmale zur Parametrisierung in globalen Agrarökosystemmodell verwendet werden können. Zuletzt werden mit Hilfe des globalem Modells LPJml5.0- tillage-cc die biophysikalischen Auswirkungen von Zwischenfruchtanbau im Vergleich zu Schwarzbrache auf die Kohlenstoff-, Stickstoff- und Wasserdynamiken abgeschätzt. Die Ergebnisse der Thesis zeigen Potenziale von und Trade-offs zwischen ackerbaulichen Bewirtschaftungsmethoden und deren globaler Modellierung auf. / Agricultural production provides a major share of food, feed, fiber, and fuel for anthropogenic usage, and is challenged by projected increasing demand due to dynamics of population growth, changes in dietary compositions, and climate change impacts. At the same time, intensive agricultural production practices have environmental externalities, which negatively affect ecosystems’ services and functions. Agroecosystem models can be used to quantify impacts of cropland use across various temporal and spatial scales, but global assessments are hampered by the limited availability of land management data and of knowledge regarding associated biophysical and biogeochemical processes and functions. The objective of the thesis is to increase the understanding of agricultural management data requirements and implications for their usages in global modeling studies. Further, the thesis aims to identify types, spatial distribution, as well as to estimate impacts, and potentials of cropland management practices to support sustainable development. In the first study, it was assessed in which way the application of different harvested crop area datasets for the national and global aggregation of modeled crop yield outputs from the grid cell to country and global scale, induces average uncertainty of ~10 % to the results. The second study presents a global classification of six soil management systems whereas the derived mapping and characteristics can be used for parameterization across a range of intensity levels in global land use modeling studies. In the third study different cropland management practices were assessed using LPJml5.0-tillage-cc, with a modified code for the representation of cover crops growing as grass on cropland between two consecutive main crop growing seasons. The thesis’ findings reveal potential and trade-offs of land management practices and their impact assessment using global agroecosystem models.