Nitrogen is an essential yield builder for crops. As such it is vital that it is not limiting, but it’s use should also be looked at carefully as part of wider cost of production considerations. We certainly don’t want to skimp on nitrogen inputs where they are most needed, but at the same time we don’t want to overapply as this means more expense for no return.

Nitrogen can be supplied to a crop naturally from the soil, as organic matter is mineralised to ammonium, followed by a microbial driven process of nitrification that converts soil ammonium (NH4+) into the nitrate form that can be taken up by a plant.

The amount of nitrogen that is supplied by the soil needs to be assessed before the correct nitrogen fertiliser rate can be calculated. The supply of nitrogen can be estimated, but the best way is to take a soil sample and have it analysed in a laboratory for soil mineral nitrogen.

The graph below shows just how much soil N can vary. Index 0 indicates low levels, while index 6 means very high levels.

Nitrogen levels also vary between individual fields in the same year due to factors such as soil type, management (e.g. manure application), or past cropping. Levels can also be different from one year to the next, with wetter seasons typically resulting in lower figures.

As a result, the amount of nitrogen available must be assessed in each year, and ideally on individual or typical indicator fields to get a true picture.

Soil nitrogen samples taken by Frontier’s precision services team over the last four years tend to show an increase in the percent of fields with a very low soil nitrogen supply (SNS) of 0.

In these circumstances, it is important that the correct amount of bagged fertiliser is used to compensate for these naturally low levels. In the samples taken, however, we can see that almost 30% of fields had a nitrogen index of 2, which would mean a reduced amount of bagged N would be needed to optimise yield.

Nitrogen levels in 2026

There are other factors that need to be taken into consideration when planning nitrogen rates too. Yield is important in this respect, as it’s directly linked to crop nitrogen demand, so an incorrect yield goal could result in under or over-fertilising.

Sometimes, such as in 2025, we may have a low yielding harvest which means less nitrogen is taken up by the crop.

The amount of nitrogen that’s been removed in the grain can be measured in the laboratory and then multiplied by yield to give the total crop N removal. In a low yielding year, because not all the nitrogen that has been applied will have been used by the crop, some residual nutrient will be left behind in the soil after harvest.

The grain results in the table below show 240kg of nitrogen was applied, but only 105kg was removed by the crop. The nitrogen use efficiency (NUE) is therefore poor, and the surplus nitrogen is high at over 100kg/ha.

This residual nitrogen will be subjected to overwinter losses related to rainfall and soil type, but a proportion will be available to the following crop.

As a result, it is important to measure or make an accurate estimate of the nitrogen in the field after winter.  Where winter rainfall quantities have been close to normal, soil nitrogen levels may be higher than expected and buck the trend of the last four years.  However, some areas that have had extremely high levels of rain recently will be much lower.  This cumulative rainfall map from Sencrop shows the amount of rainfall recorded across the country in the period since 1st January up to 12th February.

Soil nitrogen sampling down to 90cm is the preferred method, but a simpler indication can be done by taking a 0-30mm sample.

Do you apply the same rate of nitrogen across all fields on your farm?

If so, you are probably not optimising applications. Fields vary with yield potential and soil nitrogen changes not only between but within fields. The insights taken from soil sampling and laboratory analysis are great methods for helping to improve the accuracy of your nitrogen rates. Historical yield maps and data can help adjust target yields, while grain samples will show if nitrogen is optimised.

Satellite imagery is also a great way to view changes in nitrogen uptake across individual fields as well as the whole farm, and changing rates based on biomass and yield potential is a great way to improve your nitrogen management.

Useful video resources

Below you can find an on-screen walkthrough of how to create your first nitrogen application plans in MyFarm.

To learn more about optimising your nutrition applications with precision technology, please speak to your Frontier advisor or get in touch by emailing info@frontierag.co.uk or calling 0800 227 445.