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The soil thermal regime is important to the soil and plant environment, being an influential factor in determining many processes in soil. / Changes in soil bulk density, soil surface reflectance and soil temperature changes with depth and time were studied theoretically and experimental as a function of variable soil properties, soil surface state, crop cover and atmospheric conditions. / A field experiment was carried out on sandy and clayey soils with each plot being subjected to a consistent tillage and fertilizer history of either conventional ploughing, reduced energy disking or zero tillage, and fresh dairy manure or manufactured inorganic fertilizer. The measured results and the quantitative models assist hopefully in identifying how soil management affects the soil thermal regime and in making cultivation management decisions. / Soil bulk density for each fertilizer type can be predicted quantitatively from input tillage energy in a linear fashion. The reflectance of the soil surface was estimated as an integrated form of the individual reflectance and the area fractions of the soil surface components, with a soil roughness correction term. This model can cover various surface situations under different schemes of soil management. A simulation model for soil temperature was developed, which can be applied to bare soil, partially crop-covered soil and completely crop-covered soil. The models can also be used as submodels or be linked to other existing models.

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No description available.

Under intensive farming, soil structure degradation and soil erosion are primarily associated with losses of organic matter. Restoration of soil structure may depend on the amount and nature of the organic amendment added. The effect of the addition of humic and fibric materials, and beeswax, a naturally occurring source of long-chain aliphatics comparable to those present in humic materials, on microbial activity and the structural properties of a waterlogged silty clay low in organic carbon was investigated. The incorporation of the fibric material increased the microbial activity in proportion to the amount of material added, whereas the humic and beeswax materials had the opposite effect. All organic materials added increased the cohesion of aggregates due to non water-dispersible cements. The fibric material was predominantly composed of polysaccharides and large quantities were required to produce a positive effect. The humic material was mainly lipids and the effect was associated with the time of incubation rather than the amount of material added. Principal-component analysis showed that the humic material was more effective at stabilizing soil aggregates than the fibric material, although the fibric material had a greater effect on the resistance of aggregates to slaking forces. Further testing with beeswax showed that the clay-associated lipids increased by 3.5-4.0 times the resistance of soil aggregates to the slaking forces, whereas the effect of hydrophobic "free" lipids was transient and accessory by coating and embedding soil aggregates.

This thesis describes a comparative study of actual and potential soil erosion in the Wilderness area of the Umfolozi Game Reserve, and a biophysiographically comparable adjacent traditional KwaZulu landuse area. Estimates of temporal and spatial variations in eroded surfaces, sparsely vegetated surfaces susceptible to erosion, and active gullies were obtained from five sets of sequential aerial photographs taken between 1937 and 1983. Estimates of the potential influence of rainfall erosivity, soil erodibility, topography, and changes in vegetation communities and landuse practices on these variations, were extrapolated from these aerial photographs as well as from maps, field surveys, records and other studies. Interrelationships between these potential influences, and the extent to which they actually contributed to the temporal and spatial variations in the three 'erosion' surfaces, were assessed visually using a geographic information systems thematic overlay technique, and computationally using a forward stepwise multiple regression procedure. / Thesis (Ph.D.)-University of Durban-Westville, 1990.