Long term effects of direct drilling and conventional cultivation on the distribution of nutrients and organic c in soils of south Western Australia

This experiment was part of a long term tillage trial designed to examine the effect of various tillage systems on the yield of wheat on a range of agricultural soils in Western Australia. A subset of results from the main experiment is presented here.This report describes the distribution of extractable P, extractable K, total N, organic C, and pH at 6 depths in the soil from 6 locations; Wongan Hills, Merredin (H) (calcic, red-brown earth), Avondale, Merredin (L) (acid, yellow earth), Esperance and Mt Barker. Three tillage systems (conventional cultivation, direct drilled with a combine, direct drilled with a triple discdrill) and 2 nitrogen rates were applied, to sites of continuously cropped wheat. Developments were monitored for a period of 9 years.The concentrations of extractable nutrients and organic C in the surface layers of the soil were generally higher with direct drilling than with conventional cultivation. Differences between treatments were generally evident within the first three years of the experiment. The effect of tillage tended to be similar at all locations except Esperance, where tillage had no effect on the concentration of extractable nutrients or organic C in the soil. Conventionally cultivated sandy and sandy clay loam soils also tended to have a slightly higher pH than direct drilled soils