Support of cane farmer trials of enhanced efficiency fertiliser in the catchments of the Great Barrier Reef

Abstract

Key Findings
1. Applying urea at N rates 20% below the 6ES recommended rate decreased cane yield in medium and high rainfall conditions. While it maintained grower profitability, the lower yield decreases mill revenue and could reduce industry profitability. The lower urea N rate performed better (e.g. greater net revenue) in low rainfall conditions, however making N rate decisions based on predicted rainfall is currently risky.
2. DMPP treated urea and blends of 20% CRF with 80% urea applied at N rates 20% less than 6ES maintained similar productivity and profitability to urea applied at 6ES.
3. EF blends with a high proportion of CRF (e.g. 1/3 DMPP with 2/3 CRF) applied at N rates 20% lower than 6ES have high fertiliser costs, which generally reduces profitability except in a few situations such as in sand and loamy soils that experience high rainfallconditions after late season fertiliser application.
Applying the same EEF blend at the higher 6ES N rate did not increase production and so was even less profitable.
4. Concentrations of N in water sampled 1 metre below the soil surface from the Urea 6ES treatment were found to be significantly greater than from EEFs and urea applied at N rates 20% lower than 6ES.
5. Indicators of NUE, such as crop N content and N uptake efficiency, were improved in comparison to Urea 6ES when EEFs are applied at N rates 20% less than 6ES.
6. Urea treated with DMPP and blends of 20% CRF with 80% urea, both applied at N rates 20% less than 6ES, can be applied at any time during the season without loss of productivity or profitability in comparison to urea applied at the 6ES recommended rate. These strategies delivered higher yields than Urea 6ES in some high rainfall situations, which was consistent with other EEF research. These findings suggest that the EEF option should be the preferred nutrient management strategy when high rainfall is expected.