March 14, 2018

How to determine the optimum N rate for cereals

By: Natalie Wood

With only 60% of winter wheat fields having an optimum N rate close to the average, better identification of how to tailor N rates is required.

How to determine the optimum N rate for cereals
How to determine the optimum N rate for cereals

The promise of an early spring following the warmest winter for a while has been knocked recently as a result of the colder weather experienced over the last few weeks. This has brought crops back in line (or in some cases behind) what would normally be expected; whilst the recent drier conditions have allowed fertiliser applications to begin up and down the country. 

Application rates for first nitrogen splits on cereals should generally vary according to the condition of the crop coming out of the winter, with higher rates for less well tillered crops, where tiller survival is of greater importance. Second dressings will be largely similar year on year, making final applications the time to adjustment the total nitrogen rate to take into account the conditions during spring. 

Use the crop as the best indicator of N uptake

Average optimum rates for winter wheat have stayed relatively flat over the last decade of trials, at 230kgN/ha, however individual sites can vary greatly from season to season. This average is a very good starting point and any adjustments in either direction need to be carefully considered and backed by sound rationale. It is difficult to understand when to make adjustments, as the main influencing factors are mineralisation and efficiency of utilisation, two variables that cannot be accurately measured. 

Using the crop as an indicator of nitrogen uptake is the most efficient means; which can either be through tissue analysis, or through the use of tools such as the Yara N-Tester. These identify the levels of nitrogen in the plant to help understand whether the crop is running short to influence final application rates and more accurate nitrogen timings.

More information on the N-Tester

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