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12 Mar 2021

A growing role for foliar N?

A growing role for foliar N?

by Arable Farming

Using nitrogen more efficiently is one of the areas growers are increasingly focusing on and, with soil-applied products vying for position with newer foliar ones, it is important to explore options carefully. Marianne Curtis finds out more.

Traditionally ureabased foliar sprays have been applied at milky ripe stage to achieve higher grain protein but more recently, urea polymer foliar products have been developed for application, starting earlier in the season, with the aim of improving the efficiency of applied N.

As government agricultural policy moves to reducing on-farm emissions of greenhouse gases, protecting groundwater from contamination and regenerating soils, there is growing pressure on farmers to adopt more sustainable farming practices.

According to Carl Gibbard, of Agro-Vital UK, careful product choice can help growers achieve more yield and better quality from less nitrogen input without harming the environment.


We know nitrogen is an extremely important nutrient for healthy crop development, but uptake can be limited if applied in sub-optimal conditions and when overused it can have negative consequences for the environment, he says.

The type of nitrogen growers use and how and when it is applied on-farm should be considered more closely if emissions are to be reduced and greater efficiencies are to be realised, he says.

Granular nitrogen is the most common form of nitrogen farmers will use, but this is often at very high volumes and is prone to leaching and volatilisation, says Mr Gibbard.

On the other hand, urea polymer fertilisers, applied as foliar nitrogen, break down to release nitrogen as amide (NH2), which plants can readily use.


The breakdown phase often happens over a period of four to six weeks, steadily providing the crop with nutrition and avoiding the ‘flush of growth often seen with granular fertilisers.

Recent trials have indicated that 7kg N per hectare from EfficieN28-t, a urea polymer applied as a foliar nitrogen fertiliser, works just as effectively as 40kg N/ha from granular nitrogen, producing strong yields and good quality, and does not leach or scorch, Mr Gibbard says.

Foliar N products offer an opportunity to ‘fine-tune N inputs, according to independent crop nutrition consultant Dr Ian Richards, with granular, soil-applied N doing the ‘heavy lifting in a fertiliser programme.


With granular N, you can put the main dressing on for cereals up to 100-150kg/ha without damaging the crop. Liquid UAN fertilisers can also be applied in quite large quantities at the beginning of the season and while some are claimed to be absorbed more quickly than granular N, there is little difference between the two forms in this respect, says Dr Richards.

He adds: Foliar N has a role later in the season where, for example, growers of milling wheat want to boost protein levels.

It can be applied at GS75 the milky ripe stage.

If you are just wanting N, the cheapest way to do this is a 20% weight by volume solution of urea.

There are formulated slow-release polymer products and others containing sulphur, magnesium or micronutrients as well as N.

Some offer reduced risk of scorch but differences in cost then come into the choice of product to use. Interest in environmental issues relating to fertiliser application, such as reducing ammonium nitrate application, is rising.

If soil-based fertiliser is applied in spring after the drains have stopped running not much is lost by leaching, if any.

If there is a bit left over in autumn it may be at risk of leaching but is usually taken up by the autumn-sown crop.

With both soil-applied and foliar urea there can be a risk of nitrogen loss by volatilisation.

The amount lost varies a lot from none to 30-40% in extreme cases.

The key is to watch the crop N requirement and make sure you do not exceed the optimum rate. The Government has recently consulted on reducing ammonia emissions from the use of solid urea on farms in England with its preferred option being a total ban, according to NFU.


However, the consultation refers to solid urea only and no ban is proposed for foliar urea, says Dr Richards.

Looking ahead, there may be a greater need for products for fine-tuning and foliar N could help growers meet environmental requirements, he suggests.

It may be used as part of an effort to make matching N requirement to crop requirement as exact as possible; there may be a bigger role for fine-tuning.

It would be nice to think that in the future N application could be more accurately defined and applied than it is now. When deciding on whether to use a foliar product, it is also worth checking buyer and end user contracts, says Dr Richards.

Some contracts specify you cannot use foliar urea.

Sometimes use of a product can be acceptable technically but may not be commercially so.

Spring barley nitrogen trial 2020

A single trial in Fife last year, run by Scottish Agronomy, looked at nitrogen use in spring barley (KWS Laureate) with the aim of investigating the impact on yield and quality of spring barley of replacing a farm standard fertiliser programme with one focusing on ‘smarter formulations.

The following programmes were trialled:

Farm standard: 232kg per hectare (34.5% N) seedbed ammonium nitrate followed by 174kg/ha (34.5% N) at GS20 = 140kg N/ha

Treatment one: 40kg N/ ha from ammonium nitrate replaced by liquid foliar nitrogen fertiliser Efficie-N28-t (7kg N/ha) at GS31.

Total nitrogen = 107kg N/ha

Treatment two: 40kg N/ ha from ammonium nitrate replaced by Efficie-N28-t (7kg N/ha) at GS39.

Total nitrogen = 107kg N/ha The results highlight the yield response to nitrogen applications at different stages of the growing cycle, says Mr Gibbard.


Despite the reduction in total nitrogen applied, the results have highlighted that yield per kilo of nitrogen has increased from 30.86kg/ha to 36.17kg/ha and 38.6kg/ ha in treatments one and two, respectively, once the yield due to soil available nitrogen is accounted for, such as untreated yield.

An increased yield response of 25% was seen when EfficieN28-t was applied at flag leaf, with the T2 fungicide timing highlighting the importance of applying fertiliser at the right time, to the right place and using the best formulation.

This is definitely something growers should bear in mind as they develop crop nutrition plans this year in order to get the best results. Mr Gibbard adds that the high nitrogen input of the farm standard programme drove up the nitrogen content of grain, making it too high for distilling.

By using smart formulations of liquid foliar nitrogen and applying these at the right time growers can reduce total nitrogen use, maintain yields and quality all while helping to protect the environment, he says.

The product is said to be similarly priced to other fertilisers on the market and does not impact nitrogen use efficiency, making it a sustainable option for farmers.

Lower N use potential with foliar fertiliser

In trials conducted by NIAB on KWS Extase winter wheat, use of a foliar N fertiliser, applied in a programme with soil-applied nitrogen gave comparable yield with significantly lower levels of N use (see table).

The trials were conducted at the Royal Agricultural University, Cirencester, comparing use of soil-based ammonium nitrate with foliar fertiliser PolyNPlus, formulated with ureic polymers, micronutrients and organic uptake enhancers.

Rosalind Platt, managing director at PolyNPlus supplier BFS Fertiliser Services, says: The agriculture industry is bracing itself for significant new strictures in the future on the type and amount of nutrients it can use to produce the same amount of crops.

In the field Duncan Lee, Ramsbury Estates, Wiltshire

The importance of being able to reduce the estates carbon footprint and the ongoing drive to improve the operational efficiency of treating crops have led Duncan Lee, farms manager at Ramsbury Estates, Wiltshire, to look at the potential of foliar PolyNPlus ureic polymer fertiliser.

Mr Lee is responsible for managing the in-hand farming and contract farming operation covering some 3,500 hectares of which 2,850ha is down to combinable crops.

Cropping includes oilseed rape, winter beans, winter rye, winter wheat, spring barley and spring oats.

The land is Grade 3 chalky clay loam.

In the existing regime, a urea/ ammonium nitrate (UAN) 30N + 12SO3 liquid fertiliser is used for all N applications, variably applied.

For winter wheat, a total of 220-260kg N/ha is currently applied.


Although Group 2 varieties KWS Extase and KWS Siskin are grown, this is mainly for other agronomic benefits as achieving the 13% protein for milling on the estate has been a challenge.

The five-year rolling average wheat yield is 9.5 tonnes/ha.

The first N application is 80-100kg/ha, made in early to mid-February, 40-60kg/ha is applied in early April with a final application of 80-100kg/ ha going on in May.

The first two applications are applied at variable rate with the last being a flat rate.

Mr Lee first began looking at PolyNPlus about four years ago.

You need to have a full leaf canopy a big target to get it into the crop to get the benefits.

It is not going to be efficient in early growth stages with low poorly tillered wheat plants or where there is not enough growth.

But for a percentage, or hopefully all, the third application, when I am brave enough, it is.

In 2019 and 2020 we reduced the third application by 50% and then applied PolyNPlus at a later stage.

We did this for a proportion of the wheat-cropped area.

There was no difference in yield which is a positive. Research carried out by NIAB at the Royal Agricultural University, Cirencester, on winter wheat in the 2019 and 2020 harvest seasons showed that, provided 140-180kg of soilapplied nitrogen is used at the start of the growing season, foliar applications of PolyNPlus can replace the third application of soil-applied nitrogen, resulting in the same yield with significantly less nitrogen.

Using less UAN in this crucial application speeds up getting some nitrogen into all crops at the right time, says Mr Lee.

Normal liquid N applications are a time-consuming and bulky operation.

On the basis of the PolyNPlus trials data this year, we will try to reduce our UAN applications on the third application even further and, in some areas, the third application will be all PolyNPlus.

With the product, once there is sufficient leaf canopy, you are not tied to a particular growth stage timing.

Because it can be tank mixed with fungicides and whatever trace elements you need, you can play around with it.

You can drip feed it in, even add it to every pesticide application with no scorch and an increase in N use efficiency, with less volatilisation, will go some way to reducing our carbon footprint. Mr Lee usually applies PolyNPlus at GS 37 but has has also applied it at GS 39 and milky ripe stage; however, to date it hasnt had a great impact on grain protein.

He says: The beauty of PolyNPlus is that once the crop canopy is sufficient you can keep applying it, keeping the crop fully N supplied. Mr Lee is also looking at the potential to reduce N application from 260kg N/ha to 200kg N/ ha or less in wheat and how the product might be used for all applications in OSR up to and including pod set.

It doesnt take much of an increase in OSR seed weight to boost yield significantly and we have seen that a late application of N at pod set can have dramatic effects on yield, he says.

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