Understanding more about nitrogen fertiliser use efficiency (NfUE) and getter soil testing, can positively impact on crop gross margins, according to a CF Fertiliser expert at last week’s CropTec event, in Peterborough.

Better knowledge about how fertilisers work allied to the critical role of accurate soil testing in optimising N applications, should be a focus for growers, said CF’s Allison Grundy.

In farm trials during 2019, a combined approach had delivered increases in margin over fertiliser costs (MOFC) of £280/ha in some crops, whilst in others 10% higher yields had been achieved when using 15% less N, said the arable agronomist.

“Whether you look at it from a production efficiency or environmental point of view, getting the most out of bought-in fertilisers will be one of the most important management areas UK growers will face in the coming years.

“Keeping N applications to the economic optimum required to deliver yield and quality whilst achieving the maximum return on investment is a key objective for all growers and understanding NfUE and the importance of soil N supply is absolutely fundamental to this,” she argued.

In simple terms, NfUE is a measure of nitrogen fertiliser recovered by the crop: “NfUE gives growers a valuable picture of how much nitrogen fertiliser is actually used by the crop and an insight into the impact their fertiliser choices are having on their production efficiency.

“It can also highlight where potential environmental concerns might lie which is an increasingly important factor in modern production.”

Trials had shown that ammonium nitrate (AN) convincingly outperformed straight urea in wheat production in terms of NfUE with an average value for Nitram (34.5%N) of 74%, compared to just 66% for urea, she added.

“This difference of 8% NfUE is the equivalent of an additional 16% total loss of N from urea and in crops with an application rate of 200kg/ha N, this would be equivalent to a loss of 32kg/ha N. In other words, simply using Nitram resulted in crops recovering an extra 16% or 32kg/ha N than they would have done with the same application rate of urea.”

Understanding the contribution soil N is making to crops was also critical: “Unlike conventional soil N tests, our CF N-Min test not only measures the soil mineral nitrogen (SMN), the amount of nitrogen in the soil at the time of testing, but also accurately predicts additionally available nitrogen (AAN) which is what will become available to the crop between the spring and harvest.

“Adding these to an estimate of N already contained in the crop gives a true picture of soil nitrogen supply (SNS). This can then be used with CF N-Calc to produce fertiliser recommendations based on yield and quality aspirations, whilst minimising the potential environmental impact and ensuring the investment in nitrogen is made full use of.

“In 2019 trials alone, we’ve had this approach increasing margin over fertiliser costs by £280/ha in oilseed rape and adding 1 t/ha to wheat yields. In spring barley, it gave a 10% lift in yields combined with a corresponding 15% drop in N requirement.

“It’s a relatively simple way for growers to increase their own production efficiency and help industry meet future environment objectives,” said Ms Grundy.