An analysis of grower soil test results from before and after the late February rains have shown the increases in soil nitrates expected from mineralisation of the organic nitrogen (N) pool. Increases of 7 – 8 mg/kg are common, and equate to an extra 9 - 12 kg N/ha in the top 10 cm.
Increases of this order are welcome and could contribute enough N to grow an extra 0.2 - 0.3 t/ha of wheat or barley yield. However, we need to keep a few important things in mind:
- Control of summer weeds is paramount to preserving mineralised N for the crop
- Nitrate N is prone to leaching losses should we be so lucky to get a wet start
- The increase in yield potential because of recharged sub soil moisture reserves. A cereal crop with a 0.5 t/ha higher yield potential needs another 20 – 25 kg N from somewhere to meet that potential and maintain protein
- Under-applying N fertiliser will erode soil organic reserves.