The influence of particle size fractions on infiltrability was investigated in soils sampled across Namibia and western South Africa. Infiltrability was determined using a laboratory technique calibrated with rainfall simulation, which measures the passage of a suspension of soil particles through a packed soil column. Water-dispersible soil particle size fractions were determined using a high definition digital laser particle size analyser. Total (calgon-dispersed) particle size fractions were determined by hydrometer. Dispersion of soil particles resulting in crust formation on the soil surface appeared to be a main mechanism reducing infiltrability. Waterdispersible clay and fine silt determined by laser analyser showed higher correlation with infiltrability (r2 = -0.43 for clay and -0.47 for fine silt) than total clay and fine silt determined by hydrometer (r2 = -0.30 and -0.28, respectively). Clay, fine silt, coarse silt, very fine sand and fine sand fractions ( 5% infiltrability was inevitably restrained. The 120-200 ìm fraction showed no clear relationship with infiltrability. It played either a plasmic or skeletal role, depending on its ratio to the 200 ìm fractions. Fine, medium and coarse sand fractions (>200 ìm) showed a probable skeletal role in soil crusts, i.e. forming pores that enhanced infiltrability. At levels >50% of these fractions, infiltrability was potentially maximal. This potentially maximal infiltrability was also explained by the concomitant decrease in plasmic fraction content with an increase of the skeletal fraction.
|Journal||South African Journal of Plant and Soil|
|Publication status||Published - 2009|