CONSERVATION TILLAGE INCREASES SOIL-WATER STORAGE, SOIL ANIMAL POPULATIONS, GRAIN-YIELD, AND RESPONSE TO FERTILIZER IN THE SEMIARID SUBTROPICS

We compared 4 tillage practices (traditional, stubble mulch, reduced, no tillage) during 10 years under rainfed conditions on an alluvial soil in the semi-arid subtropics of central Queensland. In the final 4 years, responses to applied fertiliser nitrogen (N), sulfur (S), and zinc (Zn) were determined. We measured soil water storage, soil nitrate accumulation, grain yield (sorghum, wheat), grain protein content, and populations of soil macrofauna, with the aim of identifying soil-conserving practices that also produce high yields of high quality grain. Stubble mulch, reduced tillage, and no tillage all outyielded traditional tillage when soil fertility was adequate. With applied N, S, and Zn, the mean wheat yields from traditional, stubble mulch, reduced, and no tillage were 2.44, 3.32, 3.46, and 3.64 t/ha, respectively. The yield responses to tillage practices were due to increases in storage of soil water or efficiency of crop water use or both. Populations of soil macrofauna averaged (per m(2)) 19 (traditional tillage), 21 (stubble mulch), 33 (reduced tillage), and 44 (no tillage). The effect of the tillage practices on soil animal populations may be a factor contributing to the measured differences in soil water storage and water use efficiency. We conclude that conservation tillage practices can greatly increase grain yields, provided crop and fallow management practices are appropriate. Potential yield advantages are realised if crop establishment, crop nutrition, and control of weeds, pests, and diseases are adequate.