Farming News - Is fertiliser really to blame for declining soil health?
News
Is fertiliser really to blame for declining soil health?
Soil health has become one of farming's hottest topics, with the decline in organic matter often pinned on modern farming practices and decades of artificial fertiliser use, particularly nitrogen. But the reality is more complex says Mark Tucker, agronomist and Yara's Food Chain Business Manager for Europe. He argues that nitrogen use and soil health should be viewed as complementary, not competing.
"First and foremost, let's think about what soil health and quality actually is," says Mark. "It has a chemical element in terms of nutrient status, a physical aspect in terms of structure – how it's made up of sand, silt, clay and organic matter – and a biological fraction, which is very much where the definition of soil health sits." Mark is quick to address the accusation that fertiliser is to blame for declining soil health. He suggests that while there may have been over-reliance on fertiliser decades ago, data suggests UK farmers have a far more balanced use of fertiliser now.
"Over the last 40 years, we've roughly halved nitrogen use as a sector across the UK." He explains. "Phosphate use is down 75%, from 40kg/ha to an average of 10kg/ha, and potassium is 66% lower than in the 1980s. It's a much more complex system than pinning the blame on one input." He emphasises.
Fault with the farming system, not the fertiliser
Mark believes the issue lies with historic farming systems rather than the nutrients themselves. "It's the system that's at fault – the monoculture, continuous cereal cropping of the past. We're now seeing a systems approach revitalised, which in some ways goes right back to Charles Townshend and the 1730s. That's really where Regenerative Agriculture started, with everything geared towards soil health and fertility, incorporating cover crops, livestock and wider rotations."
Manures alone can't do the job
Rebuilding organic matter is where the debate gets complicated. Manures and compost remain the most effective route, but Mark points out that supply is limited, or in the wrong place. "Over the same 40-year period we've been reducing fertiliser use, we've lost 30% of the national cattle herd, 12% of our sheep and 41% of our pigs." This means manure is scarce or isn't always where it's needed: phosphate from livestock manures is concentrated in the west, while the need – arable farming – is more concentrated in the east.
One solution is digestate, and more anaerobic digesters are coming online, but targeting use is key. "It comes back to understanding your farm at field level," Mark explains. "Soil analysis is the benchmark for working out where organic material will have the greatest impact, whether that's for NPK fertility or for improving soil structure."
Where manures, digestate or compost aren't available, cover crops and green manures offer a way to build organic matter from within the farming system itself.
Quality matters too. "Check the source of any material coming onto the farm," Mark warns. "With concerns growing around forever chemicals in sewage-derived products, it's important to look at certification and analysis, so you know exactly what you're introducing. Otherwise, you could be building up an unintended legacy issue from what was a genuinely positive plan to improve organic matter."
Straw, tillage and cover crops
Incorporating straw brings its own short-term challenge. "When you load the soil with fresh organic material, it gets the bugs and soil biology going, and that activity consumes some of the available nitrogen." says Mark. Classically this can be seen as a yellowing in early established oilseed rape, where chaff spreading has been poor. "It can be concerning at the time but it's temporary," explains Mark. "The nitrogen cycle re-establishes within a few weeks and the crop greens up again."
On reduced tillage, Mark points to on-farm evidence from the Allerton Project at Loddington, Leicestershire, which is researching the effects of different farming methods on wildlife and the environment. Although the Allerton Project is shifting to less and less tillage to improve organic matter, they've still had to plough occasionally to get a seedbed and establish a crop. However, data shows that this occasional ploughing hasn't been detrimental to the organic matter they've built.
"Some soils tolerate zero-till easily, others are much more challenging, and farmers need to stay flexible. Light soils are genuinely difficult to build organic matter in, while heavier soils offer more opportunity. The direction of travel is towards minimal or zero-till, but the occasional plough, when the season demands it, isn't going to undo that progress."
Complementary, not competing
Asked to sum up, Mark is clear that the two sides of the debate need to work together. "The number one message is that we shouldn't pitch nitrogen against soil health. A report by Nature highlighted that judicious nitrogen use and organic matter should be seen as complementary elements. Build organic matter through the right practices and you get a more successful, better-established crop with a bigger root system, which in turn improves nitrogen use efficiency."
He also points to long-standing Rothamsted research showing that fertility built through organic matter is more available to an establishing crop than nutrients locked in the soil's chemical fraction. "Organic matter is fundamental," he adds. Drawing on his own Nuffield Scholarship findings, Mark recommends farmers develop an integrated soil fertility management plan spanning at least ten years. "These aren't quick fixes. Having that plan in place really focuses the mind on how you manage fertiliser use, soil fertility and organic matter together for the benefit of soil health."
"First and foremost, let's think about what soil health and quality actually is," says Mark. "It has a chemical element in terms of nutrient status, a physical aspect in terms of structure – how it's made up of sand, silt, clay and organic matter – and a biological fraction, which is very much where the definition of soil health sits." Mark is quick to address the accusation that fertiliser is to blame for declining soil health. He suggests that while there may have been over-reliance on fertiliser decades ago, data suggests UK farmers have a far more balanced use of fertiliser now.
"Over the last 40 years, we've roughly halved nitrogen use as a sector across the UK." He explains. "Phosphate use is down 75%, from 40kg/ha to an average of 10kg/ha, and potassium is 66% lower than in the 1980s. It's a much more complex system than pinning the blame on one input." He emphasises.
Fault with the farming system, not the fertiliser
Mark believes the issue lies with historic farming systems rather than the nutrients themselves. "It's the system that's at fault – the monoculture, continuous cereal cropping of the past. We're now seeing a systems approach revitalised, which in some ways goes right back to Charles Townshend and the 1730s. That's really where Regenerative Agriculture started, with everything geared towards soil health and fertility, incorporating cover crops, livestock and wider rotations."
Manures alone can't do the job
Rebuilding organic matter is where the debate gets complicated. Manures and compost remain the most effective route, but Mark points out that supply is limited, or in the wrong place. "Over the same 40-year period we've been reducing fertiliser use, we've lost 30% of the national cattle herd, 12% of our sheep and 41% of our pigs." This means manure is scarce or isn't always where it's needed: phosphate from livestock manures is concentrated in the west, while the need – arable farming – is more concentrated in the east.
One solution is digestate, and more anaerobic digesters are coming online, but targeting use is key. "It comes back to understanding your farm at field level," Mark explains. "Soil analysis is the benchmark for working out where organic material will have the greatest impact, whether that's for NPK fertility or for improving soil structure."
Where manures, digestate or compost aren't available, cover crops and green manures offer a way to build organic matter from within the farming system itself.
Quality matters too. "Check the source of any material coming onto the farm," Mark warns. "With concerns growing around forever chemicals in sewage-derived products, it's important to look at certification and analysis, so you know exactly what you're introducing. Otherwise, you could be building up an unintended legacy issue from what was a genuinely positive plan to improve organic matter."
Straw, tillage and cover crops
Incorporating straw brings its own short-term challenge. "When you load the soil with fresh organic material, it gets the bugs and soil biology going, and that activity consumes some of the available nitrogen." says Mark. Classically this can be seen as a yellowing in early established oilseed rape, where chaff spreading has been poor. "It can be concerning at the time but it's temporary," explains Mark. "The nitrogen cycle re-establishes within a few weeks and the crop greens up again."
On reduced tillage, Mark points to on-farm evidence from the Allerton Project at Loddington, Leicestershire, which is researching the effects of different farming methods on wildlife and the environment. Although the Allerton Project is shifting to less and less tillage to improve organic matter, they've still had to plough occasionally to get a seedbed and establish a crop. However, data shows that this occasional ploughing hasn't been detrimental to the organic matter they've built.
"Some soils tolerate zero-till easily, others are much more challenging, and farmers need to stay flexible. Light soils are genuinely difficult to build organic matter in, while heavier soils offer more opportunity. The direction of travel is towards minimal or zero-till, but the occasional plough, when the season demands it, isn't going to undo that progress."
Cover crops require the same field-by-field thinking. "Picking the right cover crop for the soil type and the moment is essential, because establishment isn't free – it costs time, money and labour," Mark says. He suggests cover crops are especially valuable after a disappointing yield, when growers expected to achieve 8-10 tonnes but only got 5 or 6. "Here there's likely to be surplus nitrogen in the field going into a typically wet August. Cover crops mop up that nutrient, reduce the risk of leaching and keep it working within the farm."
Asked to sum up, Mark is clear that the two sides of the debate need to work together. "The number one message is that we shouldn't pitch nitrogen against soil health. A report by Nature highlighted that judicious nitrogen use and organic matter should be seen as complementary elements. Build organic matter through the right practices and you get a more successful, better-established crop with a bigger root system, which in turn improves nitrogen use efficiency."
He also points to long-standing Rothamsted research showing that fertility built through organic matter is more available to an establishing crop than nutrients locked in the soil's chemical fraction. "Organic matter is fundamental," he adds. Drawing on his own Nuffield Scholarship findings, Mark recommends farmers develop an integrated soil fertility management plan spanning at least ten years. "These aren't quick fixes. Having that plan in place really focuses the mind on how you manage fertiliser use, soil fertility and organic matter together for the benefit of soil health."