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02 Mar 2022

How to fine tune your fertiliser this season.

As featured in Arable Farming Magazine

How to fine tune your fertiliser this season

by Arable Farming Magazine February issue

Record nitrogen prices will leave growers juggling to maximise crop profitability. Alice Dyer gets some advice from the experts.

Over the past nine months fertiliser prices have skyrocketed, and with summer gas futures still indicating four times to five times higher than in previous years, the trend looks set to continue.

What goes up must come down eventually, but even for growers who bought nitrogen for a good price this year, next season prices are still likely to remain higher, says Jo Gilbertson, AIC head of fertilisers.

Can we see light on the horizon? Obviously as gas prices eventually come down, it will become more economic to manufacture fertiliser, but at the moment a lot of fertiliser plants in Europe have reduced or stopped production because they cannot afford to manufacture it, she says.

Similarly, it is about supply and demand farmers are not buying at the moment because the ones with crops in the ground have bought and are covered and farmers are putting off making a decision, hoping the price will come down the gas price might be an indicator to suggest this might not happen soon.

Europes dash to reduce its carbon dioxide profile has left British farmers highly sensitive to gas price movement and with such high dependency on low-price fertilisers, they are in a vulnerable position.

Break-even ratio Amid the high prices, AHDB and ADAS have been working to create new recommendations for nitrogen management.

This starts with accommodating a new break-even ratio beyond which the value from the extra grain produced does not pay for the extra nitrogen applied to achieve it (see graph, below, right).

Since 2008, the recommendations have used a break-even ratio of 5kg of cereal grain paying for 1kg of fertiliser nitrogen, but the high fertiliser prices mean a new, larger break-even ratio has been created.

Prof Roger Sylvester-Bradley, head of crop performance at ADAS, says: It will depend on how much you paid for the fertiliser, but generally weve worked out if the price ratio has gone from 5kg of grain to 10kg, which is the current ratio, you need to reduce nitrogen applications to cereals by 50kg per hectare.

For oilseeds the ratio has changed from 2.5kg of seed paying for 1kg of nitrogen, to 4kg so that would mean also reducing nitrogen applications to OSR by 50kg/ha roughly.

This should be taken from the least effective timing which, for feed cereals and malting barley, tends to be the latest application, says Prof Sylvester-Bradley.

For milling wheat, there is a question of whether you should be cutting back at all because you stand to risk losing your premium if youre committed to a certain spec, such as 13% protein.

If youve got a very forward OSR crop then you dont need to apply nitrogen early.

Pull back across the board then you are just pulling back from that last little bit of yield you would have gained by applying the last 50kg/ha nitrogen.

Yield effects of reducing nitrogen can be modest (see table, top right).

This is because most nutrition programmes operate around the flatter part of the nitrogen response curve, meaning there can be quite big changes in nitrogen rate around the optimum ratio which only have a moderate effect on the overall yield.

Alternative sources of nitrogen will also find their value this season, with products that boost nutrient uptake becoming more cost-effective.

However, although there are a number of mainstream fertiliser options available which can help to replace bagged nitrogen, Agrovista has never found anything in its trials that would substitute more than around 40-50kg/ha of nitrogen, says head of soil health, Chris Martin.

Slow-release So, we still need around 150kg/ha as a base level from traditional sources.

One of the most popular options is slow-release fertilisers such as MZ28 which is foliar urea with different polymer length chains this means the N is released at different stages into the crop.

Agrovista started looking at this about 20 years ago, not as a cheaper form of nitrogen but as a more environmentally-friendly form of nitrogen to reduce nitrate and greenhouse gas emissions it works out several times lower in its carbon footprint than traditional fertilisers.

Current costs mean it is very cost-effective too. In the current market we will be looking for the last 40-50kg/ha on a feed wheat with 28-35 litres/ha of MZ28 at roughly around growth stage 32.

For growers applying digestate or slurries, a nitrification inhibitor is well worth considering, Mr Martin adds.

Particularly for digestates, where a lot of the N is in the ammonium form, which is very stable, the idea is to keep it in that form for as long as possible and slow down conversion to nitrate where it can be lost through leaching or as nitrous oxide.

Bacteria These include products such as N-Lock and Instinct, which inhibit the multiplication of the bacteria that convert ammonium to nitrate.

This is nothing new, but 30 years of research has shown reductions of 50% in nitrous oxide emissions and 16% in leaching that means youre getting more value from your organic fertilisers, so it would be a sensible approach this year, Mr Martin says.

Another product Mr Martin has explored, namely from a soil health point of view, is molasses and yeast extract-based L-CBF Boost.

Its basically a carbon source. Were seeing quite clearly that because youre putting a carbon source alongside your nitrogen, the amino acids are being formed more efficiently so youre getting better value for your nitrogen.

With a standard rate of about 40 litres/ha on a cereal crop across the season, you could be looking to reduce your nitrogen by 30-40kg with the same yield results.

And finally there is the increasingly popular biologicals route, utilising free living bacteria that can fix nitrogen.

Mr Martin says: There is plenty of nitrogen in our soils and around 70,000 tonnes of inert N gas above every hectare that we cant use, but we can try and reach it like a legume crop would.

Significant There are free living bacteria specific to each crop that can convert some of that into plant-useable sources. With the likes of Smart Rotations and Plant Works, were looking at some products where significant nitrogen can be fixed from the right bacteria.

While these products could hold merit in some systems, the starting point should be ensuring plants have access to the whole ‘cocktail of nutrients needed for optimal growth.

If one nutrient is missing it is going to impact the rest of them.

Molybdenum is an element we barely consider on cereals, but it is really important for nitrogen metabolism.

You may only need one atom of molybdenum for every million atoms of nitrogen, but if you havent got it, you are compromising the nitrogen because it wont metabolise efficiently.

Mr Martin recommends soil testing followed by in-season tissue or sap testing to match nutrition to the crops direct need.

In-season tissue testing is really useful because it tells you where you are on that day, where you should be on that day, where you should be at the next growth stage and how to get there.

It is one of the most comprehensive ways to match nutrition to need.

Another options is to do a ‘post-mortem with a grain test.

That will tell you how successful your nutrition programme has been.

Although it is hindsight, you can learn from it next year if there are areas you are getting horribly wrong, says Mr Martin.

More info

To help growers calculate their economic optimum for fertiliser application, AHDB has developed a nitrogen fertiliser adjustment calculator for cereals and oilseeds, based on the revised figures in RB209.


In the field Andy Howard, Kent

After completing a Nuffield Scholarship in 2016, Kent grower Andy Howard set himself the goal of reducing his on-farm inputs by 10% each year, for five years.

This has been exceeded by taking a holistic approach, incorporating good soil health, wider and more diverse rotations, regular testing and cover cropping, among other things.

However, with prices as they are this season, Mr Howard plans to tighten his nutrition programme even further.

He says: Our nitrogen strategy this year will be quite different because of the price. We have only bought one load of AN, whereas we normally buy three. The second dose of nitrogen is going to be from digestate and the later doses are going to be with foliars, which are much more efficient straight onto the leaf, meaning you need a lot less. We have been playing around with foliars and digestate but this year we have been pushed into going the whole hog. If it works, I can hopefully get rid of that one lorry load of nitrogen left.

His focus on improving soil health over the years has meant that soils deliver around 50kg/ ha of nitrogen a year alone.

It all starts with the soil. With 5% organic matter and good aeration, if youve got that, its a start, he says.

We do tests for nitrogen as well.

I used to do a Haney soil test from the US, which gives the amount thats in the soil and an estimated release.

This year Im thinking of using an available active nitrogen test which gives a prediction of what you will receive so you can remove that from your N total, but the starting point was the soil.

Tissue testing is also carried out at every important growth stage or seven to 10 days before going through with a nutrition spray.

Snapshot These have worked quite well but they are just a snapshot. This season Im planning sap tests which are a bit more in-depth and give guidance on what is happening in the next week or 10 days, as well as Brix testing, more for plant health. I also have a handheld N-Sensor which I use as more of a guide.

Mr Howard is also exploring how precision technology can work in favour of crop nutrition, taking part in the N2Vision project which aims to eventually create per plant crop nutrition applications using drones and field robotics, to boost yield and reduce nitrogen use.

I think this blend of biological and technological is the future.

The farm has used ‘bugs in a jug for five years now, giving variable but valuable results each season.

Mr Howard says: Like all biologicals, you never quite know what youre going to get.

I can almost guarantee I will get 30kg/ha of nitrogen from them in a growing season, but it might be 100kg/ha.

However, these products need to go into a healthy soil with air otherwise they will just die when they go in there.

This year I am going to be trialling compost extracts with the drill which Im hoping will help to reduce N even further.

For growers looking to go down the same route, Mr Howard says: Your soils are addicted to nitrogen, so it is important not to go cold turkey.

We have achieved this slowly, and key to this is that it was not just one single thing that has allowed this to happen.

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