How foliar feeding maintained grass growth at half N rate
The herd at Pisgah Farm © Aly Balsom Dairy farmer Robin Nicolson has halved nitrogen use on grazing leys while maintaining annual growth at 12t/ha dry matter by foliar feeding instead of using conventional, prilled fertiliser.
Foliar feeding is commonly used in horticulture and arable systems and works by applying liquid nitrogen directly to the leaf, where it is absorbed through the leaf’s pores.
This contrasts with conventional application, where a solid prill is applied to ground, washed into the topsoil by rain, and taken up by the plant’s roots.
See also: How to improve livestock soils with biological approach
Farm Facts Pisgah Farm, Pembrokeshire
Robin Nicolson with the Tow and Fert machine © Aly Balsom
- 182ha grassland farmed including a 65ha ryegrass and white clover grazing platform
- 230 Holsteins and Holstein cross Jersey cross Norwegian Red
- 6,500 litres a cow a year at 4.5% fat and 3.6% protein
- Supplying Arla
- Dedicated silage ground, mainly permanent pasture with some short-term Italian ryegrass leys
In 2019, Robin was one of four farmers to sign up to a three-year European Innovation Partnership (EIP) Wales project looking at foliar feeding on grassland.
This involved using urea and humic acid as a liquid foliar feed.
It was mixed on farm by dissolving the prilled products in water and applied using a conventional sprayer (see “How to mix a liquid foliar feed”).
This method was compared with conventional prilled N. Both were applied every 21 days and results compared against a control using no N.
Data from Pisgah Farm’s trial field – which was north facing and at 274m above sea level – showed it was possible to grow 12.5t dry matter (DM)/ha using 245kg N/ha applied conventionally, or just 92kgN/ha with foliar feeding.
Consequently, Robin invested in his own specialist foliar sprayer and switched to foliar applications on grazing ground.
Over the past four years, he has produced an average 12t DM/ha, using 100-120kg N/ha – down from 200-250kg N/ha – spread at 20kg N/ha at each application.
Nitrogen use efficiency
Numerous factors such as soil compaction, soil temperature and rainfall influence how well N is used when applied conventionally. This means utilisation efficiency can be about 50%.
In comparison, rates as high as 95% can be achieved with foliar application because N is absorbed directly through the leaf, says Nigel Howells of Nigel Howells Consultancy, who ran the EIP project (see “Tips for foliar spraying”).
Robin says this made the decision to move to foliar feeding easy.
“If you can grow the same amount of pasture with half the nutrition used, it’s a no-brainer,” he says, adding that improved efficiency likely means more nutrients are being used by the plant rather than lost to the environment.
He is also convinced of the merits of foliar feeding on silage swards. The strategy has enabled N use to be reduced from about 300kg N/ha a year to 140kg N/ha across four cuts.
Grass is “primed” with slurry after cutting to grow leaf and then foliar fed within two weeks.
Consultant Nigel Howells (left) and Robin Nicolson © Aly Balsom
Application rate
Robin has found 20kg N/ha to be the sweet spot on silage ground, as urea takes too long to dissolve at 25kg N/ha with his size of machine.
However, the lower rate does not deliver enough growth in one application, so two of 20kg N/ha are made one week apart.
However, the EIP trial found it was possible to apply higher rates, of 46kg N/ha for each cut, in one go when pre-mixing and filling a conventional sprayer.
With his son, Torin, away in New Zealand, and short-term labour challenges, Robin has temporarily stopped foliar spraying on silage ground because of time constraints.
Instead, a contractor has been used to apply liquid fertiliser to the ground. The intention is to return to foliar spraying of all grassland in 2025.
How to mix a liquid foliar feed
Ready-made foliar feed products are available, but most are designed for slow release over four weeks on arable crops.
This makes them unsuitable for grazing or silage ground with fewer than six weeks between cuts.
As a result, consultant Nigel Howells says it is better to create a bespoke mix on-farm.
- Conventional prilled urea can be dissolved in water with humic acid (protected urea is not suitable) to produce humate.
- Urea becomes volatile in solution but can be stabilised with humic acid, which also helps the foliar spray stick to the plant and promotes absorption.
- When using a conventional sprayer, create a pre-mix by, for example, dissolving the urea and humic acid in an IBC before transferring it into the sprayer.
- Humate can be bought as a dry or liquid product, but this is more expensive. When using prills, dissolving them in warm water works well.
- Agitate the mix using a cordless drill with paint mixer attachment, or a water or slurry pump, to ensure the product dissolves.
- A specialist Tow and Fert machine, designed specifically for foliar feeding, has an inbuilt agitator, so the mix can be made in the machine and held in suspension. Robin Nicolson says his machine cost about £27,000, and not having to prepare a pre-mix saves about half a day for each silage cut. “It was quite easy to make that decision [to buy] when the price of fertiliser was so high. I’d still do it today, but the payback would be longer. But there are other benefits, as you can put other things in the Tow and Fert,” he says. These include seaweed and Epsom salts.
Tips for foliar spraying
1. Try out foliar spraying on silage ground first as that has the biggest nitrogen demand.
2. When creating a pre-mix for conventional spraying, ensure the mix is well agitated so the product is thoroughly dissolved.
3. Be patient when applying – foliar feed must be applied to the leaf so should not be used immediately after cutting. In a 21-day grazing rotation, foliar-feed 10 days post-grazing and graze again at day 21.
On silage ground, apply slurry or dry fertiliser on day one, foliar-feed on day 14 and cut on day 26-plus.
The EIP trial found that N levels in the leaf peaked and dropped more quickly after foliar feeding compared with conventionally applied N.
In fact, N was used up within 10 days of application. This meant grass could be cut for silage four days earlier.
4. Not all dry humates have the same dissolvability, so assess the product and ideally choose one with more than 95% dissolvability.
5. Avoid foliar feeding in very sunny weather, as this can cause scald and reduce grass growth. In hot conditions, apply early in the morning or later at night.
Equally, do not apply when raining, as the product needs two hours to dry on the leaf.
The numbers
- £26 Cost/ha for each application of foliar feeding on grazing ground at Pisgah Farm versus £43/ha using conventional application*
- +2-3% Additional amount of sugar in fresh grass from foliar-fed silage leys, compared with ground that had conventionally applied nitrogen
- +0.8t Extra yield from foliar-fed grass given in dry spring of second year of trial (dry matter/ha)
- *Costs at Pisgah Farm during trial including urea at £360/t and contractor application costs