Key Points
- The value that soil mineral nitrogen (N) tests provide to accurate fertiliser calculations are demonstrated over four seasons. Optimal applied N rates can be decreased significantly with higher soil mineral N contents.
- Between 290 and 330 kg/ha N (soil + applied) produced the optimum yield and protein combination for the best margin in Amarok gristing wheat with a yield potential of 12 to 13.5 t/ha.
- Incorporating a late application of N at GS59 to the standard GS32 & GS39 split to increase protein content did not improve margins.
- The margin over N cost (MONC) was highest at $3,437/ha in 2005 due to the large yield increase to applied N when soil mineral N was minimal.