Ways to keep up crop yield and quality without losing soil fertility
GroundCover™ Issue: 4
Deciding on your best option for maintaining and restoring soil fertility depends on the farm's history of cropping, paddock by paddock.
Nitrogen fertiliser application provides a realistic option for maintaining crop yield and quality where structural degradation is minimal and where rainfall is reliable. Trials indicate 40-50 per cent increases in both yield and quality.
But while fertiliser can supply the needs of the immediate crop, it is less likely to restore fertility than other options.
Reduced or zero tillage
Reduced or zero tillage reduces the rate of organic matter decomposition. The best effects are being achieved when crop residues are retained and nitrogen fertiliser is applied.
The contribution of grain legumes to the restoration or maintenance of soil fertility in the long term depends on their nitrogen-fixing capacities and their net contribution to the nitrogen balance of the soil-plant system, after nitrogen is removed in the grain of the legume crop.
In chickpea-wheat rotations, wheat yields have increased up to 60 per cent following chickpea. But the long-term value of this rotation to restoring soil fertility is not yet proven.
The nitrogen benefit from legumes can be maximised by such practices as reduced or zero tillage, intensive cereal cropping to reduce nitrate-nitrogen, addition of cereal crop residues, and short fallows. The farmer needs improved chickpea varieties with the ability to fix atmospheric nitrogen in the presence of nitrate-nitrogen.
Benefits to wheat yields and grain protein levels following lucerne, medic and mixed grass-legume pastures can exceed 40-50 per cent. The long-term benefits to soil fertility increase with the length of the pasture rotation.