How a farm cut nitrogen by 60kg N/ha with no yield detriment
© MAG/Emma Gillard An Oxfordshire farm has successfully slashed nitrogen rates by 60kg N/ha with no yield detriment thanks to the addition of a carbon rich crop spray and urease inhibitor to each liquid fertiliser pass.
Piers Cowling, farm manager of Sparsholt Manor Farms near Wantage, says the tank mix extras are helping promote nitrogen use efficiency, reduce the risk of scorch and improve soil health.
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Not only have rates been cut from 220kg N/ha to 160kg N/ha in just three years, but the frequency of spray passes has dropped.
What was previously a three-spray fertiliser programme is now two, helping manage workload in busy periods as well as cutting fuel and labour costs.
The resulting improvement to crop and soil health enabled Piers to significantly cut back on synthetic fungicides and replace them with biological sprays.
Last season, a biological approach for T0 and T1 applications was adopted across the farm’s entire 600ha wheat area.
Piers also successfully grew a fungicide-free wheat crop which came with a £60/ha saving where biologicals where applied instead.
Molasses spray
On a mission to improve soil health, Piers came across the Agrii-Fortis Carbon Protect crop spray four years ago and decided to jump right in and start using it.
“We have been using liquid fertiliser for many years at the estate and were looking for ways to enhance N uptake and make each application kinder to the plant.
“We’ve included the molasses spray in all fertiliser tank mixes at 5 litres/ha for four years now,” he says.
The spray is a molasses based liquid with a 23% carbon content. It acts as a chelating agent to aid uptake and efficacy of nutrient applications, explains Alistair Hugill, commercial manager of product manufacturer ED&F Man,
“When mixed with liquid fertilisers, Agrii-Fortis can minimise the risk of scorch.
“It also helps balance soil microbial populations and can be directly applied to stubbles to support soil borne bacterial communities,” he says.
Tom Perrott, fertiliser specialist at agronomy group Agrii continues that sugar in molasses is a rapidly utilisable energy source for soil microbes.
“Adding sugars to soils can increase microbial activity in the rhizosphere, helping to balance soil carbon to nitrogen ratios and promote soil organic matter.”
This in turn increases mineralisation rates of organic nitrogen from soil bacteria, which makes more nutrients bioavailable to the plant, continues Alistair.
“Carbon:nitrogen ratios are noticeably more balanced across the soils on the estate, with ratios of 10-12:1, which is right where we want it to be,” says Piers.
Soil organic matter levels at Sparsholt have increased by 2% since 2018, with levels now in excess of 5%.
This is testament to a combination of the crop spray, chopping straw, cover cropping and reduced cultivations.
From left, Tom Perrott, Alistair Hugill, Piers Cowling and Iain Richards © MAG/Emma Gillbard
Reducing fertiliser splits
Key to the reduction in overall fertiliser use was the removal of the third spray pass.
A series of tramline trials and yield mapping data gave Piers the confidence to drop the third spray at growth stage 35-37 and roll out 160kg N/ha across the entire 600ha area of winter wheat.
“Dropping the final fertiliser spray eliminated the risk of flag leaf scorch. It also helped us offset the extra costs of the molasses spray and the inhibitor.
“Fewer passes also comes with a carbon-saving benefit and fewer machinery hours,” he says.
“I’m keen to expand the trials further this year and plan to go even lower with N rates as we have not reached breaking point yet,” says Piers.
Five-year average winter wheat yields are 8-9t/ha, with crops destined for the feed market.
“We would all love to grow 10t/ha wheat crops, but the truth is we grow 8-9t/ha wheats far more economically and more environmentally friendly.
“This gives us greater margin and more scope to sell carbon credits,” he adds.
The previous nitrogen dose rate of 80, 60, 60kg N/ha was replaced with two 80kg N/ha hits applied at the end of February/beginning of March and during the second week of April at growth stage 31.
The farm is located 800ft above sea level on an exposed site, so it often takes crops longer to get going and build biomass in the spring, especially with later-drill dates for blackgrass control.
Two early doses of N gives the plants the boost they need, explains the farm’s Agrii agronomist Iain Richards.
“What’s more, the inclusion of the inhibitor keeps the nitrogen where we want it to be,” he says.
Agrii’s liqui-safe urease inhibitor, which comes with a high carbon content to support microbial activity, is used.
Synthetic fungicides vs biologicals
Piers is now replacing synthetic fungicides with a trio of biological sprays applied at the traditional spray timings.
“We have been trialling fungicide-free wheat for three seasons now, usually splitting blocks of a variety to compare biological to synthetic programmes,” he says.
In all cases there has been no statistical difference between yields, which have been in the range of 8-10.5t/ha depending on the variety and season.
“The knowledge and experience we have gained led us last spring, with little overwinter disease present, to adopt a biological approach across the board for T0 and T1 applications, with subsequent applications reverting to synthetic products primarily in response to rust being present.”
Piers also successfully trialled a winter wheat crop last year with 100% biological sprays, which came with a £60/ha saving.
Yellow rust tends to be the biggest disease issue at Sparsholt Manor Farms.
Septoria is less problematic due to the later drilling window and carefully selected varieties, with good early vigour and disease resistance.
“If we see disease creeping into the crop, we will follow up with the chemical can and revise this at the next spray timing,” says Iain.
Varieties include Extase, Cranium, Palladium, Beowolf and Oxford.
“We’re finding Extase is becoming the dirtiest variety for yellow rust, while brown rust is Cranium’s weak point. Palladium is certainly the standout variety for vigour – even in a December drilling window,” says Iain.
Carbon credits at Spharsholt Manor Farms, Oxfordshire
Spharsholt Manor Farms generated £18/ha of carbon credits in 2023, as the estate continues to lower crop inputs and build soil health.
In 2017, when the first carbon audit was carried out, the farm was calculated to be emitting 0.43kg of carbon for every 1kg product produced.
From then, farm manager Piers Cowling began reducing cultivations across the farm and in 2022 the carbon emissions produced from the farm had reduced to 0.32kg of carbon for every 1kg product produced.
Today, fertiliser rates have been substantially cut and the estate has shifted heavily towards a direct drilling system.
Carbon emissions are projected to continue to fall, with 2027 emission figures predicted to be just 0.17kg carbon for every 1kg product produced.
Piers is auditing and selling his carbon via the soil carbon platform Soil Capital.
This is sold into the carbon insetting market which Piers believes is a more ethical way of selling carbon as it remains within the agricultural supply chain.