Summary

The effect of growing cotton-based crop rotations on cotton yield and the physical and chemical properties of a rain-fed, grey cracking clay was evaluated from 1996 to 2004 near Warra in south-east Queensland. The objective of this research was to evaluate which of the selected cereal and leguminous rotation crops, which included some used frequently in this region, resulted in the greatest benefits to the soil and to the following cotton crop. The crop rotations used in this experiment were:

• (a) continuous cotton;
• (b) cotton-sorghum;
• (c) cotton-wheat double cropped;
• (d) cotton-chickpea double cropped followed by wheat;
• (e) cotton-wheat.

Until 1996, land preparation was with conventional tillage. Thereafter, all crops were sown with zero tillage except for cultivation with a chisel plough to about 0.07-0.1 m after cotton picking to control heliothis moth pupae. The key soil properties measured were soil structure (porosity and stability), plasticity, linear shrinkage, pH, sodicity and organic carbon.

Among rotation crops, soil compaction was reduced (i.e. porosity was increased) most by sowing wheat. The shift from conventional to zero tillage also influenced soil structure with effects being more pronounced than those of the crop rotations. Although differences among rotations were small, sodicity was reduced most by the crop rotation which included the legume chickpea. Lowest cotton lint yield occurred with cotton-sorghum. A wheat rotation crop is more likely to improve soil quality and cotton lint yield than sorghum.