EFFECTS OF TILLAGE, STUBBLE, GYPSUM, AND NITROGEN-FERTILIZER ON CEREAL CROPPING ON A RED-BROWN EARTH IN SOUTH-WEST QUEENSLAND

We describe effects of a range of fallow and crop management practices on soil properties and crop growth in wheat and grain sorghum on a re d-brown earth in south-west Queensland. Results from the first 4 years of the experiment, which commenced in 1983, have been published. This paper reports results from the next 6 years. No tillage (NT) and redu ced tillage (RT), combined with stubble retention, resulted in better soil-water storage during fallow but less soil nitrate-nitrogen (N) at sowing than observed with more frequent and aggressive mechanical til lage treatments such as discing, and stubble removal. In drier growing seasons, when N application often resulted in yield reductions in whe at, NT and RT with stubble retention resulted in higher grain yields t han other treatments in both crops. In a wetter growing season, when N application resulted in yield increases, wheat yields under NT and RT with stubble retention were lower than those of other treatments, eve n at the highest rate of N application, indicating that factors such a s plant disease were also affecting yields. With stubble retention, av erage yields of 6 wheat crops were 12% higher under NT and reduced bla de tillage, and average yields of 4 sorghum crops were 20-30% higher u nder NT, than other tillage treatments. Gypsum application resulted in an average yield increase of 15% in both crops under conventional dis c tillage with stubble retention. In wheat, NT and RT with stubble ret ention were generally associated with lower grain protein concentratio n, and N application was necessary to maximise profitability of these practices.