The physical clay particle content of the clay layer is 55%~60%,and that of the loam layer is 35%~50%. The thickness of clay layer get smaller and smaller from upper reaches to lower reaches.
The correlation coefficients of slope gradient with clay particle, organic matter and total N in sediment were -0.9832, -0.9395 and -0.8146 , respectively.
The results of correlation analysis between SAP content and soil particle composition showed that, in 1982, there were highly significant negative correlation between the SAP and soil sand particle (20.02mm) content, and highly significant positive correlation between the SAP and soil clay particle(<0.002 mm), while no significant correlation between the SAP and soil silt particle(0.020.002mm).
The case was different in 2002, SAP was significantly negatively correlated with soil sand particle content, and highly significantly positively correlated with soil silt particle content, while not significantly correlated with soil clay particle content.
As far as soil texture is concerned, the content of silt particles is highest with the average of 45.03% and the content of clay particles is lowest with the average of 24.69% in every soil separates.
Of which, soil clay grain, organic matter, soil water, total nutrient, quickact nutrient, biomass and photoefficiency decreased separately by 84.3%,65.5%,74.8%,9.25%~72.8%,27.5%~69.9%,60.5%,56.8% and soil temperature raised by 0.9℃ in serious desertificed farmland.
Results of correlation analysis showed that a decline in crop production caused mainly by a decrease in content of water content, quickact N in soil(correlations coefficients were 0.920 2,0.942 5 separately), a decline in soil water content was closely interrelated with deflation of clay grain and organic matter from soil(correlations coefficients were 0.953 4 and 0.963 8 separately).
The porosity and percentage of tiny sand (diameter 0.05-0.1 mm) and clay particle (diameter >amp;lt; 0.05 mm) increased, bulk density in surface soil decreased, and saturated water-holding capacity improved.
The consolidation tests indicated that the vertical strains of undisturbed soft clay could be divided into three stages with load increasing, however, the remolded clays were almost independent of stress level.
The two cut-off points of these three stages are the preconsolidation stress and the structural yielding stress of the original clay, which could be determined by shear wave velocity measurement.
The strains developed during cyclic tests of undisturbed and remolded soft clay, both having one turning point under different amplitude of cyclic stress.
The porosity and percentage of tiny sand (diameter 0.05-0.1 mm) and clay particle (diameter >amp;lt; 0.05 mm) increased, bulk density in surface soil decreased, and saturated water-holding capacity improved.
In order to assess how this rapid urbanisation process impacts the environment, 106 silt and clay (particle size >amp;lt;0.053?mm) samples, separated from Gaborone surface soil samples representing urban, agricultural and rural sites, were investigated.
It is shown that the complexation of oppositely charged polyelectrolytes on the surfaces of clay particles intensifies the flocculation of clay-salt dispersions.
The successive adsorption of oppositely charged polyelectrolytes strongly affects the flocculation due to the formation of polyelectrolyte complexes on the surface of clay particles.