Applying nitrogen (N) at multiple times during the season can better match crop demand, minimise risk, and increase returns. Mid-season is a good time to reassess crop N needs.
There are a variety of tools to help growers estimate crop N needs. Most use a budget where the N rate is the difference between N demand (driven by yield) and N supply from the soil. Expected yield is the biggest driver behind many of these tools. This means the key input of an N budget is often ‘best guess’. If yield is over estimated money is wasted on excess N. If yield is underestimated, money is left on the table with reduced yield or grain quality.
Without a crystal ball, there’s no getting away from estimates in crop nutrition. One way to reduce the risks of using estimates is to simulate different outcomes.
Simulate mid-season N rates
Paddock variability can have a huge impact on how profitable fertiliser N is. However, a single estimated yield is often used for a whole paddock or farm. Rather than choosing one yield for your N budget, use a range.
Using yield maps, divide paddocks into different yield zones. Then assign a yield range to each zone. The low yield zone may be 1.0 – 1.8 t/ha, the medium zone 1.5 – 2.5 t/ha and the high zone 2.0 – 3.5 t/ha. Run different yield scenarios for each zone to understand how much N you need to apply in each.
Using the outputs of the tool, base the N rate for each zone on:
- the most likely yield
- how much N may be wasted or yield lost if the N rate targets a higher or lower yield, and
- how this affects return on investment (ROI) on N.
Checking mid-season N supply
Use soil tests to check current soil N stocks. N-rich test strips help you follow in-crop N supply.