Around 25–30% of nitrogen (N) applied to paddocks is lost each season in the northern region. Researchers are not recovering this nitrogen from the soil or the crop biomass.
Isotope labelled 15N fertiliser is used to track fertiliser nitrogen through the cropping system. Field trials in NSW and Queensland with sorghum crops examined:
- fertiliser rates
- nitrification inhibitors
- timing of nitrogen application.
Denitrification causes most of the loss. Low oxygen soils with labile organic matter and available nitrate are most at risk.
Graeme Schwenke is a NSW DPI research scientist, based in Tamworth.