A thesis submitted to the Faculty of Science University of the Witwatersrand, Johannesburg for the Degree or Doctor or Philosophy October 1987 / A t h r e e - y e a r study was un dertaken in the semi-arid (500mm p a . ) n o rth -eastern lowland area of South Afric a. All the woody plants were removed from one -hectare savanna plots on three d i f f e r e n t soil types , and key hydrological and biological changes were monitored relative to adjacent controls. Runoff increased initially, but decreased once the grass cover increased. Deep drainage and lateral subsurface flow increased on the sandiest site. Evaporation from the soil surface increased on the heavier t e x t u r e d soils. The duration of plant - available water in the soil increased on all cleared p l o t s . & The p re - c l e a r in g woody plant abo veground biomass was in the range of of which 0 . 6 6 to 0 . 8 0 t ha was 5.6 to 11.2 t ha -1 leaf biomass. The annual herbaceous production was stron gly rainfal' dep endent, averaging 1 to 1.5 t ha -1 , and increased by 0 . 4 - 0 6 t .ha -1 except on the most f erti le site ( 0 . 6 - 2 0 t ha ) . Total available forage increased with c l e a ring, but so did its variability The observed changes in herbaceous layer palatability could not be a t trib u t e d to clearing. Woody plants and grasses wore shown to have w a te r- u s e niche separation in both rooting depth and time of water use. Simulation over forty years of wetting patterns indicated 75 to 85 % niche overlap, w t h separation on the depth axis more important in sandy sites, and on the time axis in clayey sites. Competition between woody plants and grasses was strongly asymmetrical in favour of woody plants. w >

From the data presented, the probable fertility level of the various soils were estimated upon the basis of the crop yield. / Master of Science

Elastic-plastic stress·strain models are developed for initially anisotropic soils. The models are developed for both total stress (undrained) analyses and for effective stress (drained) analyses. For anlsotroplc undralned coheslve soils under monotonic loading an elastic-plastic isotropic-hardening model is developed. For complex loading conditions the model is extended using multisurface plasticity. For effective stress analyses of soils, the Cam-Clay model concepts are generalized for initially anisotropic soils. Both isotropic and anisotropic hardening are used in the model. The behavior of the models is investigated under several loading conditions and some comparisons are made with experimental triaxial data. A nonlinear three-dimensional finite element program is developed in which the models are implemented. An updated Lagrangian large displacement analysis is also included. The constitutive models developed are used to investigate the influence of initial anisotropy on the bearing capacity, deformation and pore pressure development under footings in both plane-strain and three dimensional conditions. It is found that for the range of anisotropy encountered in the field, the deformation and bearing capacity are significantly different. / Ph. D.

No description available.

No description available.

It was found that Azotobacter vinelandii grown in a dialyzed soil medium did not fix nitrogen and had a much lower rate of respiration than when grown in Burk's nitrogen-free medium. When para-hydroxybenzoic acid served as the added oxidizable organic carbon source in dialyzed soil medium, the azotobacter grown in it were found to be unable to fix nitrogen. On the other hand, A. vinelandii fixed nitrogen when grown in soil supplemented with glucose. It was concluded that natural conditions in the soil are not conducive to nitrogen fixation by A. vinelandii.

Ng Chi Chung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 126-143). / Abstract --- p.i / Acknowledgements --- p.iii / Lists of Tables --- p.vii / Lists of Figures --- p.ix / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Importance of soil physical properties to plant growth --- p.2 / Chapter 1.3 --- Importance of organic matter to soil physical properties --- p.5 / Chapter 1.4 --- Chemical composition of sewage sludge and spent sawdust litter and their disposal --- p.6 / Chapter 1.5 --- Objectives --- p.9 / Chapter 1.6 --- Significance of the study --- p.10 / Chapter Chapter 2 --- Literature Reviews / Chapter 2.1 --- Influence of organic wastes on soil organic matter --- p.12 / Chapter 2.2 --- Influence of organic wastes on soil aggregate stability --- p.15 / Chapter 2.3 --- Influence on bulk density and total porosity --- p.21 / Chapter 2.4 --- Influence on field capacity and water holding capacity --- p.23 / Chapter 2.5 --- Influence on soil water intake and in situ soil moisture content --- p.27 / Chapter 2.6 --- Influence on mechanical resistance --- p.28 / Chapter Chapter 3 --- Methodology / Chapter 3.1 --- Study site --- p.30 / Chapter 3.2 --- Treatments --- p.30 / Chapter 3.3 --- Soil sampling --- p.32 / Chapter 3.4 --- Methodology / Chapter 3.41 --- Organic carbon --- p.33 / Chapter 3.42 --- Aggregate stability --- p.34 / Chapter 3.43 --- Bulk density --- p.37 / Chapter 3.44 --- Field capacity --- p.37 / Chapter 3.45 --- Water characteristics curve --- p.38 / Chapter 3.46 --- Infiltration --- p.38 / Chapter 3.47 --- Water release property --- p.39 / Chapter 3.48 --- Mechanical resistance --- p.39 / Chapter 3.5 --- Statistical analysis --- p.39 / Chapter Chapter 4 --- Effect on Soil Aggregate Stability / Chapter 4.1 --- Introduction --- p.41 / Chapter 4.2 --- Results / Chapter 4.21 --- Effect on soil organic matter content --- p.45 / Chapter 4.22 --- Change in organic matter content under continuous cultivation --- p.46 / Chapter 4.23 --- Effect on aggregate stability under continuous cultivation --- p.47 / Chapter 4.24 --- The relationship between percentage aggregate stability and the amount of organic matter --- p.49 / Chapter 4.3 --- Discussion --- p.52 / Chapter 4.4 --- Conclusions --- p.60 / Chapter Chapter 5 --- "Effect on Bulk Density, Total Porosity and Mechanical Resistance" / Chapter 5.1 --- Introduction --- p.62 / Chapter 5.2 --- Results / Chapter 5.21 --- Change in bulk density and total porosity --- p.65 / Chapter 5.22 --- Change in bulk density and total porosity under continuous cultivation --- p.66 / Chapter 5.23 --- Change in bulk density and total porosity in relation to organic matter content and aggregate stability --- p.67 / Chapter 5.24 --- Change in mechanical resistance --- p.69 / Chapter 5.3 --- Discussion --- p.71 / Chapter 5.4 --- Conclusions --- p.77 / Chapter Chapter 6 --- Effect on soil water retention / Chapter 6.1 --- Introduction --- p.80 / Chapter 6.2 --- Results / Chapter 6.21 --- Field capacity and change between the second and the fourth harvest --- p.82 / Chapter 6.22 --- Relationship between field capacity and organic matter content --- p.84 / Chapter 6.23 --- Water characteristics curve --- p.84 / Chapter 6.24 --- Change in water characteristics curve between the second and the fourth harvest --- p.88 / Chapter 6.25 --- The relationship between water holding capacity and organic matter content --- p.91 / Chapter 6.26 --- Change in available water capacity and its relationship with organic matter content --- p.92 / Chapter 6.3 --- Discussion / Chapter 6.31 --- Change in field capacity --- p.95 / Chapter 6.32 --- Change in water holding capacity and available water capacity --- p.97 / Chapter 6.4 --- Conclusions --- p.100 / Chapter Chapter 7 --- Effect on Infiltration and Water Release Property / Chapter 7.1 --- Introduction --- p.102 / Chapter 7.2 --- Results / Chapter 7.21 --- Infiltration and its change under continuous cultivation --- p.103 / Chapter 7.22 --- Water release property --- p.109 / Chapter 7.3 --- Discussion --- p.112 / Chapter 7.4 --- Conclusions --- p.117 / Chapter Chapter 8 --- Conclusion / Chapter 8.1 --- Summary of findings --- p.118 / Chapter 8.2 --- Implication of the study --- p.122 / Chapter 8.3 --- Further studies --- p.123 / References --- p.126

Thesis (Ph.D. (Agriculture)) --University of Limpopo (Turfloop Campus), 2005 / Drying, grinding and sieving are commonly employed to facilitate the handling, storage of soil samples on which chemical, biological, and physical analyses are to be performed. These laboratory protocols have the potential to alter soil chemical characteristics and may result in unrealistic estimates of in situ chemical processes. The effect of laboratory soil sample preparation on level of extractable Ca, Mg, K, and P was determined. The analyses were done on laboratory prepared soil samples and compared with the characteristics of fresh soil samples (field-moist) for the same soils that were sampled in pairs of 20 per location of the four locations. Samples were collected at Tshiombho irrigation scheme, Dal water farm, Magoebaskloef pine tree farm and Syferkuil experimental farm. The results indicated that soil samples should be kept at their field moist status until experimental procedures are done. Concentration of most extractable ions for the two preparation methods correlated closely. However, grinding and air-drying increased P concentration by 1.3 to 1.55 times, and decreased the concentration of K by 2 to 2.5 times and this is caused by soil moisture depletion. According to the results, there should be different preparation methods for different extractable ions, Ca and Mg can be continued analysed on laboratory prepared soil samples but soil pH, K and P should be analysed on fresh soil samples. If such is not done, then the effects should be considered when interpreting the results for fertilizer recommendations. / NRF

Forensic taphonomy is concerned with investigation of graves and grave sites. The primary aim of forensic taphonomy is development of accurate estimations of postmortem interval (PMI) and/or postburial interval (PBI). Soil has previously been largely ignored, therefore this thesis is designed to investigate changes in decomposition as imparted by the soil. Furthermore the impact of cadaver interment on the surrounding soil may offer prospects for identification of clandestine graves. A series of laboratory controlled decomposition experiments using cadavers (Mus musculus) and cadaver analogues (skeletal muscle tissue (SMT); Sus scrofa, Homo sapiens, Ovis aries and Bos Taurus) were designed to investigate decomposition in burial environments. Sequential destructive harvests were carried out to monitor temporal changes during decomposition. Analyses conducted included; mass loss, microbial activity (CO2 respiration) and soil chemistry (pH, EC and extractable NH4 +, NO3 -, PO4 3- and K+). Several experimental variables were tested; frozen-thawed versus refrigerated SMT, different mammalian sources of SMT, different soil type and contribution of soil versus enteric microbial communities. Mass loss measurements for SMT experiments demonstrated a sigmoidal pattern of mass loss, however, larger cadavers (Mus musculus, 5 weeks) did not. The inhumation of SMT (frozen, unfrozen, different mammalian sources) or cadavers leads to an increase in microbial activity (CO2 respiration) within 24 hours of burial. A peak of microbial activity is attained within a week, followed by a decrease and eventual plateau. The rapid influx in microbial activity is matched by corresponding increases in pH and NH4 + concentration. pH and NH4 + are strongly correlated in soils with acidic basal pH, by comparison highly alkaline soil demonstrated no relationship. NH4 + concentration also appeared to be related directly to NO3 - concentration and cadaver or SMT mass. A decrease in NH4 + corresponds with an increase in NO3 -, however, nitrification was unpredictable. Rapid nitrification was observed in sand systems when SMT was interred, but was not noted when cadavers were interred. By comparison both sandy clay loam and loamy sand soils demonstrated rapid nitrification after inhumation of a cadaver. When cadaver or cadaver analogue mass was larger, so were NH4 + and NO3 - concentrations in systems that experienced nitrification.

No description available.