T he last 12 months has provided another reminder, if one were needed, of how quickly farm economics can change; further proof of the need to react and refine to optimise farm performance in the face of continuing market and climate volatility.

And that is what a number of farmers have been doing with a series of variable rate nitrogen trials in winter oilseed rape (WOSR) and winter wheat.

The aim is to evaluate optimum nutrient use efficiency (NUE) and margin over input cost (MOIC).

But escalating N costs have brought that more into focus, with many farmers wondering just how low they can go.

The group is using Bayers FieldView to evaluate the trials, with last seasons results throwing up some surprises when it comes N rates.

Certainly, that is how Robert Burden, of Chilbridge Farm, Dorset, sees it.

In the past adjusting N rates to crop biomass has always paid dividends, but last season the work threw up a different result.

He compared rates ranging from 20% below to 10% above his typical winter wheat treatment of 230kg N/ hectare.

He applied four programmes with total volumes of 180/200/230 and 250kg N/ha, the second application being the one where rate was varied.

The result surprised him as the higher the loading of N, generally the better the result.

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

But recalculate those figures on the current fertiliser price of £2/kg and that investment score shifts depending on field and variety.

In one field, the best return remained with the highest loading, but in others 230kg N/ha produced the best MOIC, and in yet another field the 250kg N/ha and 200kg/N/ha applications came out equal.

The WOSR result is probably best described as ‘neutral the higher rates and resulting yield being cancelled out by increased input costs, although in the highest biomass areas the lower rates did deliver a small improvement in yield and MOIC.

Mr Burden is a little puzzled by both results and his conclusion is ‘more work is needed.

With the rape he suspects the variability in results 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.

Useful

Some might see this as a wasted exercise, but Mr Burden does not.

It is another piece of data in the library that might be useful in the future.

He says: Rarely are two seasons alike.

Im building up data over several seasons which I can use to refine future decision making.

Its not just about improving NUE and MOIC but also our farm footprint.

And he still made savings across some parts of the farm.

In one WOSR field FieldView satellite imagery showed areas of low crop biomass.

Mr Burden decided to drop the final N application, and that paid off as although yield was impaired the crop returned a respectable margin.

Interestingly, his results from the 2021/22 season reflect those seen by others in the group.

The results from Stockbridge, Hampshire-based Simon Gents WOSR trials also show no real gain last season from varying fertiliser rates to reflect crop biomass.

On his farm, although the variable rate areas brought input savings, the overall result was a 0.1 tonnes/ha yield loss, and with rapeseed priced at £508/t Mr Gent was worse off to the tune of £20/ha.

But caution is needed.

For the purpose of the trial, the group decided to continually cut back on the higher areas of biomass and divert more nitrogen to the thinner areas.

This goes against the standard convention of loading final N rates to higher biomass areas where the crop has the greater yield potential.

Interestingly, where higher rates were used on the low biomass areas, there was an additional return of £91.51/ha compared to the standard flat rate.

Shropshire farmer Andrew Williamson also saw higher N rates deliver last season.

He has been adjusting N rates on the back of N-Min tests, with volumes typically ranging between 200-240kg N/ha.

But he wondered whether rates could be tweaked a little lower.

Using a field of first wheat Graham, he compared his ‘typical rate of 220kg N/ha to a rate of 160kg N/ha.

FieldView analysis showed a significant yield difference between the two treatments, with the higher rates of N delivering the higher yields.

Mr Burden says FieldView opened his eyes as to what was possible on-farm.

He feels it takes farm trials to almost academic standard.

He considers that even with combine yield monitoring, accurately overlaying yield data with variable rate mapping was not really possible.

But FieldView has changed that and allows him to do this even with small or irregular field areas.

Quality

More important is the quality of that data.

He wants comprehensive stats before coming to any firm conclusions.

He says: Im able to pull out data precisely from any plot area regardless of size or shape.

It means theres no ambiguity with the data Im evaluating important if Im to make exacting decisions.

And I can review that data real-time if needed giving me more time to think about my options.

Mr Williamson shares this view.

He is looking to refine all parts of his farming operation and is a keen advocate of farm trials, combining his data with other independent sources.

FieldView offers significant benefits, key of which is the ease with which field performance data can be accessed and evaluated as he is able to pull data from any ‘as planted or ‘as applied pass.

But it also simplifies monitoring trial field areas or tramlines.

Mr Williamson does not 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.

Its perfect for anyone who likes to do their own trials, he says.

Bayers Max Dafforn says: Building up layers of data can only help farmers plan better to manage risk, whether that is market, inputs or weather driven.

FieldView users will have a bank of historic data they can call upon combined with up-to date in-field monitoring from the Field Health images.

This can be used to better inform in-season decision making based on the particular conditions for that season.