Measurement and simulation of void structure and hydraulic changes caused by root-induced soil structuring under white clover compared to ryegrass

Re-packed soil columns of the Crediton series were sown with white clover or perennial ryegrass, with nitrate managed according to organic and conventional farming regimes respectively. Visual observations revealed a rapid enhancement in soil structure beneath white clover compared to ryegrass and unplanted soil. Enhanced structural differentiation beneath white clover was supported by greater permeability to air and freer drainage to water. Differences in soil structure were verified by water retention measurements over a range of tensions between the wilting and gravity drainage points. The void structure was simulated with the Pore-Cor network model, which verified larger pores beneath clover, a difference in local structuring and a saturated hydraulic conductivity which was four times greater than ryegrass. The study highlighted inadequacies in current approaches to the measurement and interpretation of water retention.