Influence of dryland agricultural management practices on the acidification of a soil profile

The high cost of transporting limestone for distances up to 300 km to acidic cropping soils in Australia has caused interest in evaluating the effect of management practices on soil acidification. Practices which minimise acidification will minimise the use and hence cost of liming. A long term rotation trial which started in 1979 at Wagga Wagga in southeastern Australia provided an ideal opportunity to evaluate the effects of some rotations, stubble handling and tillage practices on the relative rates of soil profile acidification over a period of 12 years, The soil had an initial pH (CaCl2) of 4.93 and 0.13% total N. All 13 treatments acidified the soil over the 12 years of the trial, at rates equivalent to a loss of 46 to 95 kg CaCO3 ha(-1) year(-1). Although there were differences between treatments in their relative rates of acidification only the management of N, as fertiliser or via legumes in the rotation, appears to offer any scope for minimising acidification rates, Most treatments influenced the stratification of the soil profile more than they influenced the net rare of acidification. All 13 treatments had minimum pH and minimum variance in pH at 5-10 cm depth, the depth range into which crop seed is generally placed. Direct drilling resulted in a higher pH (CaCl2) at 0-5 cm depth than conventional (2 or 3 passes) cultivation but the reverse was true at 5-10 cm, Direct drilling resulted in a stratification of soil pH which was exaggerated by burning stubble, as opposed to retaining it, and minimised by an increasing intensity of cultivation. There was no difference in soil profile acidification between lupin crops (Lupinus augustifolius), L, and subterranean clover pasture (Trifolium subterraneum), C, in 1:1 rotations with wheat (Triticum aestivum), W. The addition of a second wheat phase, LWW, made no difference to the soil pH compared to the LW rotation. The effects of mowing and mulching of subterranean clover on soil pH were not significantly different to the effects of grazing by sheep.