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CAFRE N-check project for wheat grain nitrogen content

Introduction

Cereal growers in Northern Ireland have to follow Fertiliser Manual RB209 recommendations for the amount of N to apply to their crops. RB209 states that grain nitrogen concentration is a “better guide than yield to indicate whether nitrogen fertiliser use is correct”. Grain nitrogen concentration recorded over a period of years can be used as justification for adjusting future fertiliser N applications.

What is N-check?

N-check is a CAFRE project run in conjunction with AFBI Crossnacreevy to assess the N content of wheat grain samples. The result of this test allows the grower to check whether the crop received too much, too little or the optimal amount of Nitrogen. A long term picture of the effectiveness of N management can be built up over several years with samples taken from wheat crops each year.

Relating grain N content to nitrogen application

For farms in Northern Ireland the guideline grain %N is 2.0% for feed wheat. If grain %N is higher than 2.1% the crop has taken up more nitrogen than needed. If grain %N is lower than 1.9% the crop needed more nitrogen than it was able to take up. Guidance given in RB209 states ‘where there is a consistent trend of low grain nitrogen over several years, then nitrogen rates should be increased’. The adjustment advised is 30 kg/ha nitrogen for every 0.1% difference in grain nitrogen from 2.0%.

Summary of N-check results 2008 to 2012

A total of 102 farmers’ samples of winter wheat grain from the 2008-2012 harvests have been analysed to date. Of these 51 had less than 1.9% N in the grain, 31 were between 1.9% and 2.1% and 21 had greater than 2.1%N in the grain.
The large number of samples with low grain %Ns suggests either the amount of N available to the crop was inadequate, curtailing yield formation, or available N was not taken up by the crop. These crops have used the N they acquired very efficiently but their yields would have been higher if they had taken up more N.
Only a small proportion (20%) of crops sampled had poor efficiency of N take up in producing grain yield. This poor efficiency could be due to any or a combination of the following factors:

• Poor growing conditions curtailing yield formation relative to the amount of N available to the crop.
• Over-application of N fertiliser or organic manure.
• Late application of nitrogen.
• Undisclosed applications of organic manure.

This is why supplying accurate information about yield and the amount and timing of fertiliser N and organic manure applied to the crop is essential as it enables better explanation of grain% N results.

Interpreting N-check results

Year to year weather variations have a major effect on the efficiency with which wheat crops use nitrogen in producing yield. Weather alongside management decisions such as disease and lodging control and the amount and timing of N applied, have to be considered when interpreting grain N-check results. For anyone interested in taking part in N-check or needing help in interpreting results please contact your local crops development advisor.
In summary, grain %N content is a valuable tool helping growers understand how weather conditions affect crop growth and yield management, enabling them to make more informed decisions about future N management.

Leigh McClean, CAFRE Greenmount and Ethel White, AFBI Crossnacreevy