Factors affecting runoff and soil loss under simulated rainfall on a sandy Bainsvlei Amalia soil

Abstract

This study was conducted on a long-term tillage experiment that was designed to evaluate appropriate tillage practices for sustainable dryland crop production. Measurements of runoff and soil loss were conducted on a sandy Bainsvlei Amalia soil (88.0% sand, 3.6% silt, and 8.4% clay) with a rainfall simulator on three tillage practices, namely no-tillage (NT), stubble mulch (ST) and conventional tillage (CT), each combined with four levels of wheat residue cover. The measurements were replicated twice for each of the three tillage practices on 1 m2 area plots. The simulator used for the study produced raindrops at a constant intensity of 60 mm h-1 with a veejet type nozzle, which had kinetic energy comparable to natural rainfall. A sharp decline in runoff and soil loss occurred with an increase in residue ground cover from bare to about 70%, above which the effect was less dramatic. Generally, runoff and soil loss was higher on NT plots compared with ST and CT plots. It is recommended that a crop residue covering at least 70% should be maintained on the soil surface when conservation tillage is practiced to ensure higher infiltration and lower runoff on this type of soil. Tilling the soil to a depth of at least 150 to 250 mm below the mulch gave the lowest runoff and soil loss.