Tillage practices and the growth and yield of wheat in southern New South Wales: Lockhart, in a 450 mm rainfall region

Abstract

Effects of tillage treatments on the wheat crop were compared during a 3-year cropping phase on a red-brown earth which had previously supported subterranean clover. Direct-drilled wheat after long and short herbicide fallows yielded as well as wheat after cultivated fallow, and differed only in terms of small reductions (averaging 12%) in early plant growth. Non-fallow direct-drill crops had, compared with fallow crops, significantly less soil water (34 mm) and mineral nitrogen (30 kg/ha) at sowing in the first season, but not in later ones. However, they always showed reduced early plant growth, averaging 28% less than cultivated crops, and despite a subsequent narrowing of relative differences in growth gave significantly lower (15%) grain yields in the two wetter seasons; only in the second year, a severe drought causing very low yields, did they produce yields equal to those of fallow plots. The use of narrow combine points in direct drilling, giving incomplete soil disturbance, gave yields equal to those obtained with standard points and complete disturbance of the soil surface. However direct drilling with retained stubble - gave lower yields in a wet season. Averaged over 3 seasons, cultivated fallow yielded 2.54 t/ha, herbicide fallow 2.41 t/ha and non-fallow direct drill with stubble burning 2.17 t/ha. It was concluded that non-fallow direct-drill yields suffered because of reduced presowing water storage and reduced early growth, the latter effect was of less final consequence when the spring was dry.