Influence of long-term wheat residue management on acidity and some macronutrients in an Avalon soil

Abstract

This study was initiated to determine the influence of different wheat residue management practices, that were sustained for about 20 years, on some fertility indicators of an Avalon soil in a long-term trial near Bethlehem in the eastern Free State. The treatments were two methods of straw disposal (burned and unburned), three methods of tillage (ploughing, stubble mulch and no tillage) and two methods of weed control (mechanical and chemical). Soil samples were collected at various depth intervals and pH, P, K, Ca, Mg and Na contents were determined. The effect of either straw burning or tillage practice on these indicators was much greater than that of weeding method. Burning of straw increased pH, P, K and Ca contents to substantial depths, although only pH and K were influenced significantly. The tillage practices affected pH significantly to 450 mm depth, with no-tilled plots having the highest pH values compared to the mulched and ploughed plots. No tillage, and to a lesser extent mulched tillage resulted in an accumulation of P, K, Ca and Mg in the upper 100–150 mm soil when ploughing served as reference. Chemical weeding also followed the same trend of accumulation of nutrients in the upper 100 mm soil when compared with mechanical weeding. This trend was also observed in pH, although it was not significant. No tillage combined with chemical weeding was the most beneficial to restrict acidification. In the case of the nutrients, significant interactions were virtually absent, except for K where burning combined with either no tillage or chemical weeding resulted in the highest K values in the upper 100–150 mm soil.