Key Points
- If N moves below the current soil sampling depth of 15cm, growers may underestimate soil N availability and overestimate fertiliser N requirements.
- Soil mineral N amount and distribution under different land uses was studied on two Waikato soils.
- On the ash soils, we found high levels of mineral N at 30-60cm under short term maize crops, probably a result of recent cultivation of pasture.
- In the peat soils, we found no increase in soil N at depth under long term maize, and growers were applying appropriate amounts of fertiliser N.
- Our results support the rainfall risk analysis which showed risk of fertiliser N leaching in Waikato is low.
- Deeper soil sampling would improve estimates of soil N availability and therefore fertiliser N requirements for maize crops.