An innovative set of trials conducted by the Agriculture Horticulture Development Board (AHDB) is examining the effect of nitrogen (N) application on yield variation.
Large variations in wheat yields across farms and fields, and even within fields, often make growers question their approach to N management.
The development trials have been established in order to help farmers test the accuracy of their fertiliser management on their winter wheat crops.
The AHDB-funded ‘LearN’ project tested a radical new approach to help farmers work out whether they were applying too much, too little or just the right amount of N fertiliser.
The project
A total of 18 highly-engaged farmers were selected to test their farms’ standard N rates in simple tramline trials. Crucially, each of these farmers already followed nutrient management best practice.
The trials, which ran from 2014 to 2017, tested single replicates of two treatments:
- 60kg/ha more than the farm standard rate of fertiliser N;
- 60kg/ha less than the farm standard rate of fertiliser N.
Each treatment was applied in alternate tramlines.
In order to justify an increasing fertiliser expenditure, a yield increase of 0.3t/ha was deemed necessary to account for an additional 60kgN/ha – based on a wheat price of £140/t and fertiliser costs of £0.70/kg.
The average wheat yield, from 142 tramline experiments, was 11.43t/ha for the farm standard.
On average, yields were reduced by 0.36t/ha for the minus 60kgN/ha treatment and increased by 0.36t/ha for the plus 60kgN/ha treatment.
Accuracy is the key
Sajjad Awan, who manages nutrient management research at AHDB, said: “On balance, there was little, if any, economic incentives to deviate from the standard N rate on these farms.
“The benefits of tramline trials depend on the accuracy of the standard N rate, as well as the accuracy of the trial.
If the accuracy is already there, then there’ll be little benefit of increasing or decreasing rates.
While the trials confirm that the standard applications of fertiliser are sufficient, they serve to provide farmers with a “piece of mind” knowing that they are taking the right approach.
“Across all experiments, none of the farmers were applying too much or too little N consistently,” said Awan, meaning that N fertiliser was not the cause of yield variation.
This means that the large variation in yield, both across farms and fields, was probably the result of agronomic, genetic, chemical, soil or engineering factors.
“It is these factors that need to be addressed, if yields are to be improved significantly,” added the researcher.
According to Awan, the best way to optimise N applications is to follow ‘The Nutient Management Guide’ (RB209) supplied by the AHDB.
“This will provide you with the tools to develop a nutrient management plan and flex it in response to the season. LearN-type approaches are most useful to deploy in fields where N optima are uncertain,” he said.
