New research confirms that varying nitrogen (N) fertiliser rates within a field result in only minor improvements to yield, gross margin, and greenhouse gas emissions compared to a flat optimum N rate for winter wheat, winter barley, and oilseed rape.
The research, conducted across 11 commercial farms in the UK over 5 years, found that on average, Variable Rate Nitrogen (VRN) applications would have increased yields by only about 0.05 tonnes per hectare and improved profits by roughly £10 per hectare. The environmental benefits of VRN were also modest, with only small reductions in greenhouse gas (GHG) emissions per tonne of crop produced.
To carry out the trials, ADAS divided single fields into hundreds of small square plots with different amounts of nitrogen applied to each plot, then fitted N response curves and calculated the “optimal” N rate for each plot. Besides N, all other inputs and applications remained the same.