Trials Show Possible Penalty With N Rates Reductions

Nitrogen prices are still squarely in the spotlight, so an ongoing trials programme with a number of FieldView users is timely to say the least.

Behind them hasn’t been the aim of cutting total N input, although no doubt welcome, but a desire to refine nutrition strategies. Matching nitrogen rates to defined soil variability is an obvious route to optimise nutrient use efficiency (NUE) and increase crop margins, but it is a complex exercise, especially where significant soil variability exists throughout a field.

One of those is Shropshire farmer Andrew Williamson. He is in the middle of a three-year variable rate trial. He has been adjusting N rates on the back of N-Min tests for some time, with applications typically ranging between 200-240kgN/ha. But always looking for further refinements he wanted to push this a little further.

Andrew Williamson

He stresses that it is early days but a limited data set has already thrown up an interesting question on how far N rates can be scaled back. Analysis using FieldView showed a significant yield difference between the two treatments applied, with the higher rates of N delivering the higher yields.

Last season he used a field of first wheat Graham, here he compared his ‘typical’ rate of 220kgN/ha with a rate of 160kgN/ha. He found that an interesting exercise itself but so was the nature of the trial, which involved a novel chequerboard approach. It was decided that because of the variability throughout the field, straight tramlines might give a skewed result. So together, Andrew, Dr Christina Baxter of ADAS and Bayer’s Max Dafforn arrived at the decision to divide the field into strips, with each strip getting a broadly equal share of the higher and lower application.

Andrew typically applies N in 3 splits, each with a generous dose of sulphur as he feels this improves mobilisation. Both treatments started with a solid application of 30kgN/ha with 40kg/ha SO3, followed by two further liquid applications of 96kgN/ha and 28kg/ha SO3 on the farm standard plots, which was compared with two applications of 64kgN/ha and 18kg/ha SO3 on the lower rate plots.

The trials continue but it does give Andrew food for thought. “It is one season’s worth of data but the best yields came from those areas with the higher N rates,” he notes.

In the past adjusting N rates to crop biomass has always paid dividends For Robert Burden of Chilbridge Farm, Dorset but his 2021/22 trial threw up a similar result, where the higher the loading of N, generally the better the result.

He compared rates ranging from 20% below to 10% above his typical winter wheat treatment of 230 kg/N/ha. He applied four programmes with total volumes of 180/200/230 and 250 kg/N/ha, the second application being the one where rate was varied.

In the wheat trial – three different fields and varieties – the higher N loading delivered the greater the yield in every case and with Robert shrewd enough to anticipate rising N prices and locking in fertiliser prices at £1/kilo the improved yield delivered the best return on investment.

But recalculate those figures on the current fertiliser price of £2/kilo and that investment score shifts depending on field and variety. In the Higher Ground field, the best return remained with the highest loading but in others 230 kg/N/ha produced the best MOIC, in another field the 250 and 200 kg/N/ha applications came out equal.

He also undertook similar trials with WOSR and the results are probably best described as ‘neutral’ – the higher rates and resulting yield being cancelled out by increased input costs.

He is a little puzzled by the results and his conclusion is more work is needed. With the rape, Robert suspects this is down to the drought. Research has shown that WOSR is more sensitive to drought than winter wheat. With the wheat trials, he feels a season of lower disease pressure may have had some influence. Higher N rates usually fuel disease pressure resulting in higher fungicide rates to preserve crop potential.

Some might see this as a wasted exercise, but Robert doesn’t. It is another piece of data in the library that might be useful in the future. “Rarely are two seasons alike. I’m building up data over several seasons which I can use to refine future decision making. It’s not just about improving NUE and MOIC but also our farm footprint.”

But he still made savings across some parts of the farm. In one WOSR field satellite imagery coming in from FieldView highlighted areas of low crop biomass. Rob decided to drop the final N application, and that paid as although yield was impaired the crop returned a respectable margin.

Research standard farm trials data

Andrew is a keen advocate of farm trials and combines his own farm work with other independent information sources. He is also a long-term member of Bayer’s Forward Farmers Group.

In the past, farm trials have often been hindered by possible data discrepancies, but he believes FieldView has changed that and proved to be an invaluable tool for a trial that was more complex than straight tramlines.

“The key thing is the data – it has to be accurate to make the right decisions. With this trial, I did omit two small field areas due to issues outside the nature of the trial and this has ‘muddied the water’ a little.

“When you’re conducting trials in an irregular field, there is always the possibility that the data might not be totally 100% true. But the margin of error with FieldView is minimal so I know the data coming back is accurate,” he says.

Andrew points to the variable N trial being a good example. “With a more complex trial like this, it’s pretty impractical to be harvesting half a tramline and then taking that off to the weighbridge. The plots are registered in FieldView and all I need to do is click on the area in question to get my data. And I can compare any field or plot area with another quickly and simply.”

Andrew also used FieldView to create the fertiliser application prescriptions, and these too are recorded in the platform. This brings all the data together in one place, useful for evaluation and administration requirements. Another plus for Andrew was that he doesn’t need canes to know where he is in the field – the FieldView cab app does it for him. “I know precisely the moment I enter or exit any plot or trial area,” he says.