Effect of tillage on rainfed maize and soybean yield and the nitrogen fertilizer requirements for maize

Abstract

Crop production in the semi-arid tropics of Northern Australia is constrained by soil erosion, variable rainfall, high temperatures and low soil fertility, especially nitrogen. A 4-year field experiment was commenced in the 1984–1985 wet season to evaluate the effects of no tillage (NT) and conventional tillage (CT) on the yield of maize grown at five levels of nitrogen (0, 20, 40, 80 and 160 kg N ha −1) in rotation with soybeans. Maize yields under NT were significantly increased by 130 and 110% over CT during the drier years of 1985–1986 and 1987–1988 compared with 11 and 8% during the more favourable years of 1984–1985 and 1986–1987. Nitrogen application significantly increased maize yields for NT in 1984–1985, 1985–1986 and 1986–1987 with an average maximum yield of 4.10 t ha −1 at the 80 kg N ha −1 application. However, under CT an average maximum maize yield of 2.82 t ha −1 was obtained at 20 kg N ha −1. This may be partly attributed to organic residues breaking down releasing nitrogen under CT or the greater soil moisture under NT improving N utilization. Soybean yield under NT was 20% higher than that under CT which was attributed to better emergence and establishment in NT. The rotation of maize with soybean had very little effect on maize yield compared with continuous maize. Maize N, P, K, S and Zn uptake was generally higher under NT for all 4 years but the uptake was significantly higher under NT in dry years. Over the 4 years total P uptake in maize (Stover+Grain) in NT was 26, 89, 14 and 51% higher than under CT indicating a significantly greater uptake during dry years. Similar trends were observed for other nutrients especially zinc.