Prevent nitrate and phosphate pollution with safer slurry spreading this winter
An expert has emphasised the critical importance of environmentally conscious slurry spreading practices this winter to protect water.
A specialist once responsible for measuring the nitrate and phosphate levels in every river and lake in Ireland, Dr Lucy Crockford now applies her expertise at Harper Adams University.
In her role as a senior lecturer in soil and water management, she helps farmers, land managers and agricultural advisers of the future to understand how to manage soils and water responsibly.
Pivotal to this responsibility is the importance of understanding what can be done to prevent contaminants entering watercourses in the first place.
As wet winter conditions bring an increased risk of nitrate and phosphate pollution in watercourses, Dr Crockford says it is crucial for farmers to follow the Farming Rules for Water to help protect the environment.
She explains: “Once water is contaminated with nitrates and phosphates, it’s very difficult to try and improve the water quality.
“An increase in these nutrients entering watercourses can lead to an increase in algal blooms, which bring a wide range of detrimental impacts.
“For example, this could result in a change in the smell and taste of the water, degrading its quality from a human health perspective.
“Algal blooms also reduce the oxygen levels in water, which can be fatal for fish and invertebrates, resulting in biodiversity loss.”
Water company Severn Trent reports that every £1 spent on helping farmers to protect and maintain water quality through catchment management initiatives results in £4 of wider environmental benefits – so prevention at source is key.
During autumn and winter, Dr Crockford says that the greatest risk of phosphate and nitrate pollution from on-farm activities comes from spreading slurry.
She says: “If farmers have struggled to spread slurry over the summer, because it’s been wet, they might be looking at very full slurry tanks at this time of year.
“There might be occasional nice days through the colder months that seem like a good opportunity to spread this slurry, but the problem is that plant growth has slowed down, so the nutrients applied to the fields will not be taken up.
“And then when it rains, the phosphates in the slurry, bound to soil particles, will be washed away into nearby watercourses, while the nitrates can leach through the soil profile, contaminating groundwater.”
Safer slurry management
The Farming Rules for Water state manure must not be spread on waterlogged or flooded ground, because of the associated nutrient loss, soil damage and run-off risks.
Nitrate vulnerable zone (NVZ) restrictions, which affect farmers in north and east Shropshire, also prevent farmers from spreading high readily available nitrogen manures through autumn and winter.
In these areas, adequate slurry storage is critical to enable farmers to store slurry until the spreading window is open again.
There are several grants available to help farmers invest in improving and maintaining slurry storage, including the third round of Defra’s Slurry Infrastructure grant, which will be available this year, and options within Severn Trent’s Environmental Protection Scheme (STEPS).
For farmers outside of the NVZs, Dr Crockford advises there are several ways to spread slurry more safely through autumn and winter.
“Firstly, consider carefully how much slurry the field actually needs,” she says.
“Before any slurry application, analyse the nitrate and phosphate levels of soils. Slurry should also be tested to understand its nutrient levels, instead of relying on a standardised value for calculating your slurry quality.”
She explains: “If you don’t know what nutrient levels are already present in the soil, it’s impossible to accurately apply additional nutrients needed.
“Overloading the soil with more nutrients that it needs leads to a high risk of nitrate and phosphate pollution through run-off and leaching.”
The Farming Rules for Water also state that when spreading, a buffer margin of at least 10 metres must be allowed near any watercourse, and 50 metres within a spring, well, or borehole.
Dr Crockford explained these margins should be biodiverse for maximum value.
“A thickly matted, biodiverse margin containing different grass and herbal ley varieties will absorb more nutrients than a traditional basic grassland mix, doing a better job of preventing potential run-off.
“These margins also improve water retention in your soils, benefitting potential crop productivity long-term.”
She also recommends exploring new innovations in slurry spreading technology, which are designed to protect soils and minimise environmental impacts.
“There have been some great advances in kit such as umbilical slurry applicators, which can inject slurry into the soil for more precise nutrient application, leaving the tanker off the field to prevent soil damage.
She adds: “It’s worth looking at different grant options available through schemes such as STEPS to help with investing in this kit – not only to help protect water quality but to look after your soils for the future too.”
Farmers in NVZs in north and east Shropshire must abide by these restrictions when spreading manures with more than 30% of their total nitrogen content immediately available to crops.
Including poultry manure and liquid organic manures (e.g. sludge, cattle/pig slurries, anaerobic digestates), this must not be spread on or between the following dates.
Grassland
Shallow or sandy soils – 1 September to 31 December
All other soils – 15 October to 31 January
Tillage land
Sandy or shallow soils – 1 August to 31 December
All other soils – 1 October to 31 January
