Fertiliser responses of wheat sown into conventionally cultivated seedbeds and direct-drilled into previously uncultivated seedbeds

Abstract

In 4 consecutive years (1980-83) on a red earth near Yass, New South Wales, 9 fertilizer treatments were applied annually to wheat which was either sown into conventionally cultivated seedbeds or direct-drilled into previously uncultivated seedbeds sprayed with herbicide. Treatments comprised 1 unfertilized control, 4 levels of P and at a moderate rate of P, 2 levels of S and 2 of N. The same fertilizer treatments were applied to each plot throughout the 4 years. The response to P was substantial, with yield increases up to the maximum rate of 37 kg of P/hathinyear. Average grain yield over 4 years was 3.2 t/ha at 37 kg P/ha and 0.5 t/ha without P. With fertilizer and grain prices that applied over the 4 years, these responses were highly profitable. There was a response to N in 1983 only (18 kg of grain/kg N) and a small response to S in 3 of the years. Yields were 17% higher under direct drilling in 1980, probably because of grassy weeds in the conventional cultivation plots. In 1981 there was no difference between the 2 tillage treatments, and in 1982-83 yields averaged 15% less under direct drilling. Although the difference between the yield of direct-drilled and conventional cultivation treatments were relatively greater without or at low P than at the highest P level, this interaction was not statistically significant.