The effects of the additions of some commonly-available organic residues to an acid, P-deficient soil (typical of those used by small-scale farmers in KwaZulu-Natal) on soil pH, exchangeable and soil solution AI, P availability and maize yield response was investigated in a number of laboratory and glasshouse experiments. The organic amendments used were ground-up grassveld residues, household compost, filter cake (a waste product from a sugar mill) and layer poultry manure. The soil used was a Hutton form (Farmingham series) (Rhodic Ferrasol, FAO). In an initial laboratory study, addition of all of the organic residues, at rates equivalent to 10 and 20 Mg ha¯¹, raised soil pH significantly and as a result there was a marked reduction in exchangeable AI concentrations. The increase in pH and decrease in exchangeable AI was more pronounced at the higher rate of addition and followed the order: poultry manure> filter cake> household compost> grass residues. The major mechanism responsible for the increase in pH was thought to differ depending upon the type of organic residue being considered. Whilst the relatively high content ofCaC0₃ was probably the main mechanism in the case of poultry manure and filter cake, the proton consuming ability of humic material probably predominated for household compost and decarboxylation of organic acids during decomposition was probably the main mechanism in the case of grass residues. Additions of organic amendments also decreased concentrations of total AI (AIT) in soil solution but the concentration of monomeric AI (AIMono) as estimated by pyrocatechol violet 60 sec. method, was unchanged or even increased. This latter effect was attributed to the high cation content of residues (particularly that of poultry manure) which increased soil salinity and exchangeable AI³⁺ was consequently displaced into soil solution.Additions of amendments also increased the Olsen-extractable P levels in the order: poultry manure> filter cake> household compost> grass residues and their addition also decreased theP adsorption capacity ofsoils. Concentrations of exchangeable Ca, Mg and K, and Na in the case of poultry manure, were increased by additions of organic amendments. In a glasshouse experiment, the four organic residues were applied to soils at a rate equivalent to 20 Mg ha¯¹ with or without the addition of either lime (equivalent to 0, 5 or 10 Mg ha¯¹) or P (equivalent to 0, 10 or 50 kg ha¯¹). Lime applications to the control (unamended) treatment resulted in a marked reduction in exchangeable AI, AIT AIMono and in the proportion of AIT present as AIMono in soil solution. The addition of organic amendments increased soil pH and reduced AIT and AIMono to low concentrations regardless of whether lime was applied or not. There was no yield response in maize to applied lime in any of the amended treatments. There was a yield increase in response to applied P in the control, household compost and grass residue treatments but none for the filter cake and poultry manure treatments. In agreement with this, Olsen-extractable P values in soils followed the order: poultry manure> filter cake> household compost> grass residues > control. It was concluded that the addition of organic amendments to acid soils is a practicable way of liming them and reducing the potential for Al toxicity and that it can also reduce fertilizer P requirements. This research now needs to be extended into the field situation. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.

Long-term environmental quality is closely linked to maintaining soil quality. Therefore, assessment of the effect of land use on soil chemical, physical and biological properties provides fundamental information about soil sustainability. The role of vegetation on soil structural and aggregate stability has received much attention over the last few decades. The loss of soil due to erosion and reduction in organic matter due to change in vegetation is usually caused by invasion of grassland by trees. The response of soils to land use depends on the inherent soil properties and environmental conditions thus the effect of land use on soil stability is site specific. The objectives of this study were to assess and compare soil aggregate stability under trees and in open grassland from open-savannah woodland and nearby deeply eroded dongas (gullies). Within the dongas, tree encroachment was expected to improve soil structural stability by increasing the organic matter content. Results that were obtained from this study are aimed at improving management of soil for smallholder and pastoral farming systems. The study site was located at Potshini, KwaZulu-Natal Province, South Africa, about 18 km south-east of Bergville. The vegetation of the area is classified as grassland biome. Acacia sieberiana var. Woodii has encroached into the valley especially onto the eroded areas. Within the study area itself the dominant parent materials are sandstone and dolerite, with colluvium covering the lower slopes. The dominant soil was classified as Hutton form. Effects of different vegetation types (grass and trees) on the soil structural stability was evaluated for their effects on soil organic carbon (SOC), mean weight diameter, bulk density, root density, clay mineralogy and some other chemical properties. For this study the site was divided into two areas i.e., the donga (D) and the grassland (G). These were then each subdivided into two parts namely, donga under a tree (DUT) with a corresponding open area (DOA), and grassland under a tree (GUT) with its corresponding open area (GOA). Three bulk samples were collected from each sampling area from 0 to 20 cm (topsoil only) using a spade. Samples for bulk density were collected from 0 - 10 cm. For soil aggregate stability determinations, samples were dried and sieved to collect soil aggregates between 2.8 and 5 mm. Some of the bulk sample was analysed for SOC, pH, exchangeable bases, nitrogen and clay mineralogy. For root biomass, soil samples were collected from 0 - 10 cm using a stainless steel cylinder of 1766 cm3 volume. The type of vegetation affected the soil physical and chemical properties of the soil in the investigated horizon (A horizon). Although the results were not significantly (p > 0.05) different, the open area showed a positive effect on soil structural stability where higher soil aggregate stability and root density were observed, as opposed to under trees in both donga and grassland. Due to the non-significant differences observed in both donga and grassland, the effect of trees and grass on the aggregate stability was considered as the positive effect. The bulk density showed an unusual trend. Bulk density was higher in the open areas where high aggregate stability was observed. From these results it was concluded that because trees have larger roots than grass these are more effective in loosening the soil particles but less effective in stabilizing the soil aggregates. In other words, the high amount of fine roots increased the soil stability while large roots improved the loosening of the soil particles. The amount of vegetation considerably affected all the physical and chemical soil properties investigated. The SOC and root density was considerably higher under grassland compared to the donga. The clay mineralogy differed between the donga and grassland. The donga soils had a higher kaolinite content and amount of interstratified smectite/mica compared to grassland. The presence of interstratified smectite/mica in the donga could cause lower aggregate stability due to shrinking-swelling cycles during wetting-drying conditions. The effects of mineralogy have been overridden by organic carbon in the grassland. From this study it was revealed that soil aggregate stability is the product of interactions between soil clay minerals, and organic fractions which are influenced by soil environment, land use and soil properties. This means that all the factors involved in aggregate formation and their stabilization are interdependent. It is suggested that factors that were driving the soil aggregate stability in the donga were different to the ones in grassland. It is suggested that the aggregate stability was driven by inorganic factors i.e., clay, clay mineralogy, bases and CEC in the donga while organic carbon and plants roots were dominating in the grassland / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

No abstract available. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.

The classification of Bioresource Units (BRUs) was developed to provide a reconnaissance appraisal of the natural resources for both environmental impact assessments and the agricultural potential of KwaZulu- Natal. Storage of the Bioresource Programme in a geographical information system (GIS) facilitates usage. Of the criteria used for the classification of BRUs, climate (rainfall and temperature in particular), was considered to be the most important factor. Other factors used were the soil association codes of the Land Types, plant indicator species and communities, and terrain type. The base map used for the study was the 1 : 50 000 topo-cadastral map on which the Land Types (LTs) were demarcated. The result of the study was the mapping of 590 BRUs, each of which is sufficiently homogeneous in environmental factors (climate, soil association, vegetation type and terrain form), such that uniform land use practices, production techniques and levels, can be defined with a reasonable degree of accuracy. Ecotopes, based on LT information, were defined for each BRU. An ecotope is a class of land, defined according to soil characteristics, within which agricultural production will be uniform and will differ significantly between one ecotope and another. The ecotopes, both for cropping and veld, are not spatially defined, but expressed as percentages of the total area of the BRU. In the BRU inventory, crops suitable for the BRU and each ecotope, and the level of production (tons/ha/annum) in the case of crop ecotopes, are supplied at a stated level of management. In addition, it is possible to investigate the potential for 29 crops for which crop production models exist, and for any other crop providing its growth and site requirements, particularly climate and soil, are known. Additional crop production models will be developed, as the demand for this type of information is high. Veld management norms, such as grazing capacity, are supplied for the veld ecotopes. On the completion of the classification of BRUs the decision was made to develop a third level of classification and the Bioresource Groups (BRGs) were mapped. In the classification of the BRUs 23 vegetation types had been identified and used as one of the criteria for BRU demarcation. By grouping all the BRUs with the same vegetation type, BRGs were defined. Each BRG, therefore, consists of a specific vegetation type containing one or more BRUs of the same vegetation type. The 23 BRGs are used mainly for regional and veld management planning. The programme was designed for use by a wide range of people with individual skills and knowledge, and contains most of the information needed for land use planning. It is essential however, to be able to identify ecotopes in the field to effectively use the information at a detailed level for farm planning. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1999.

Rural farmers in the Nkwezela Area, with an average family size of 10 people, face a number of problems. The crops that are predominantly cultivated in the area, for subsistence (maize, dry beans, sorghum, potatoes, cabbages and turnips) have very low yields compared to the potential yield of the land. Natural resources in the area are increasingly deteriorating. In addition, arable land has shown remarkable signs of soil erosion that may lead to loss of soil fertility. This study evaluates the current land suitability for subsistence agriculture in Nkwezela based on climatic, soil, topographic and crop requirement data collected from different sources. The spatial parameters of the land resources were digitally encoded into a GIS database to create thematic layers of the land resources which was then compared to the crop requirement data of the selected crops grown in Nkwezela namely, maize, sorghum, dry beans, potatoes, cabbages and turnips. A GIS was used to overlay the thematic layers of the resources to select areas that satisfied the crop requirements of the selected crops. The results of the analysis of the land evaluation in the study area showed that the very hot summers, very cold winters together with the high clay content in the soils are the two limiting factors in Nkwezela. The land suitability maps indicate that sorghum is highly suitable in the area with dry beans and maize being relatively suitable. Cabbages are the least the least adapted crop with potatoes and turnips being not suitable due to the high temperatures during the growing season and the very cold winters. In conclusion Nkwezela is in a high rainfall area that is suitable for subsistence agriculture where warm season crops like dry beans, maize and sorghum are used for daily consumption by the community and can be cultivated in a sustainable manner. In addition the correct farming methods, procedures, liming and fertiliser requirements must be implemented, adhered to and maintained in order to improve crop yields in a sustainable manner and to encourage subsistence agriculture by the community. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

The physical and chemical properties of soils can greatly influence the vegetation patterns in a landscape. This is especially so through the effect that particular characteristics of soils have on the water balance and nutrient cycling in savanna ecosystems. Areas in the savanna environment found in Hluhluwe iMfolozi Park have experienced a number of changes in the vegetation patterns observed. This study, therefore, looks at the effect that soil characteristics may have on the vegetation growth in this area and on the changes that have taken place over time. Fixed-point photographs, taken every four years, were used to choose fourteen sites in the Park, which showed either a ‘change’ or ‘no-change’ in vegetation from 1974 to 1997. The sites consisted of four which had ‘no-change’ in vegetation, two sites with a slight increase (5- 20%) in tree density, three sites with a greater increase in tree density (>20%), two sites with a slight decrease in tree density (5-20%), and three sites with a greater decrease in tree density (>20%). Transects were then carried out at each site, in which the soil was classified to the form and family level. Each horizon was then sampled and the field texture, structure, Munsell colour and depth of each horizon and profile recorded. The data recorded in the field were statistically analysed through a principal component analysis (PCA). The type of horizon, horizon boundary, structure type, colour group and depth for the top and subsoil were included in the models and were analysed with the number given to each site for each of the three sections of the Park, namely Hluhluwe, the Corridor and iMfolozi. The most prominent textures at all sites were sandy loam, loam, clay loam and silt loam for both the top and subsoil for all site categories. The texture classes were also compared across the Hluhluwe, Corridor and iMfolozi sections. The dominant textures in the Hluhluwe and Corridor sections are loam, clay loam and silt loam for both top and subsoils. Sites sampled in the iMfolozi section appear to have textures mainly associated with the clay loam and sandy loam classes. The structure classes of the soil including sub-angular blocky, granular and crumb which are associated with a moderate structure appear to be the most dominant type in all categories for the topsoil; single-grain and sub-angular blocky classes the main types for the subsoil. Generally the colour of the soil at all the sites sampled was yellower than 2.5YR and the values and chromas mostly fell within the range of 3-5 and 2-6, respectively. This is also shown in the PCA results obtained, which associate particular soil characteristics with the various sites sampled for the different vegetation change categories investigated. The samples collected were also analysed in the laboratory after being air-dried. The laboratory analysis included measurements of pH, exchangeable acidity, organic carbon, extractable phosphorus, particle size distribution and cation exchange capacity (CEC). The data recorded in the laboratory were also analysed by PCA. This was used to determine which soil properties are associated with the particular sites investigated. The pH of the soil, in all areas, fell within a wide range. The pH is influenced by the rainfall in the area and thus sites sampled in the Hluhluwe section are more acidic than those sampled in the Corridor and iMfolozi sections. The topsoils had a higher pH for all the samples and were in the range between 5 and 7. The exchangeable acidity measurements were low, although they were higher in the subsoil as opposed to the topsoil. The nutrient contents did not appear to vary greatly between the different sites in the Park. Generally extractable phosphorus, CEC and organic carbon were low across the Park. The particle size analysis showed that the clay percentage increases between the top and subsoil for all the sites sampled. The silt and various fractions of sand percentages vary across all sites and are lower than the clay percentage at all sites except the A horizon of the ‘slight increase’ sites. The ‘no-change’, and ‘increase’ sites have a higher percentage of clay as compared to the silt and sand fraction for both the A and B horizon. The ‘slight increase’ sites have a higher percentage of sand in the A and B horizon, the ‘slight decrease’ sites have a more equal percentage between the sand, silt and clay fractions in the A horizon and a greater percentage of clay in the B horizon. The ‘decrease’ sites have a greater percentage of clay and silt in the A and B horizon. While certain soil properties have a definite effect on the plant growth, no relationship between specific soil properties and vegetation changes was shown. However, it is likely that the soil structure and texture affect the vegetation patterns, through their influences on the water and nutrient holding capacity. With an increase in the clay percentage and more strongly structured soils, plants can access more water and nutrients and this will increase the tree density in an area. However, the recent changes in the vegetation patterns observed in the Park appear to be more associated with other environmental factors. The soil properties analysed would have generally been more constant at the sites sampled, particularly over the relatively short period of time in this study. Therefore, the changes which were recorded in the fixed-point photographs would have been enhanced by other factors experienced in the Park, including fire and the effect that grazers and browsers have on the vegetation. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.