Influence of mono- and biculture cover cropping systems on soil polysaccharides and aggregate stability in a sandy loam Oakleaf soil in Eastern Cape, South Africa

Abstract

Mono- and biculture cropping systems are thought to affect aggregate stability by influencing soil polysaccharides but the exact relationship is uncertain. The objective of this study was to determine the effects of cover cropping systems on polysaccharides and aggregate stability in an Oakleaf soil. Two experiments involving a cereal, two legumes and a weedy control, either in mono- or biculture, were done. The crops were oat (Avena sativa L.), vetch (Vicia dasycarpa L.) and lupin (Lupinus angustifolius L.). All cover crops in both cropping systems increased soil polysaccharides. Cover crops in both systems improved aggregation either by increasing macroaggregates and/or lowering the percentage of the 0.25–0.106 mm aggregate fraction size. The mean weight diameter increased under the mono- but not biculture system. The hot-water extractable polysaccharides fraction was actively involved in aggregation in the Oakleaf soil. The correlation between hot-water extractable polysaccharides and the mean weight diameter was negative (r= −0.55) for the monoculture system and positive (r= 0.71) for the biculture system. Microaggregates coalesced even when such increase in size did not trigger a significant increase in the mean weight diameter. Secondly, microaggregates also seemed to serve as building blocks for macroaggregates.