Since the introduction of the first Nitrate Vulnerable Zone measures in 1985, the use of mineral nitrogen has been halved in Denmark, while fertiliser efficiency has almost doubled to 40%.
But, while this might be good news for the environmentalists, farmers were less happy, as yields had remained virtually unchanged over the same period, Kent Myllerup Jensen from the Danish Agricultural Advisory Service told the AICC conference.
“All farmers are afraid to break the rules, otherwise they face a stiff penalty. Most use advisers to ensure their paperwork and calculations are correct.”
Much of the groundwater was used for drinking without cleaning, so it was crucial for the authorities to avoid nitrate pollution, he said.
A number of rules had been introduced and subsequently amended since 1985, covering everything from the capacity of manure or slurry storage, spreading technique, and cover crops But one of the biggest, and perhaps most contentious issues, was the “mineral nitrogen quotas” imposed on every farm, he explained.
The overall quota was based initially on a standard crop nitrogen quota, which – against the wishes of farmers – had been set at 10% below the economic optimum level. “Farmers were unhappy about this and are still fighting for a higher quota,” said Mr Jensen.
This figure was then corrected to account for the weather (typically ±5-10kg/ha of N) and the effect of any catch crop in the previous year was also subtracted. Finally, a correction was made to account for the actual usage of animal manure, eg 75% for pig slurry, 70% for cattle slurry and 40% for sewage sludge.
As an example, a typical winter wheat crop on loam soil (15-25% clay), yielding 8.5t/ha had a mineral nitrogen quota of about 171kg/ha, Mr Jensen said. “Farmers have to pay more attention to optimising nutrient usage. The timing of fertiliser applications is important, which is why many are investing in 12 months of storage. Many spring-sown crops are sown with foot [seed-bed]-placed N and site-specific application of nitrogen using yields monitors and soil analysis is important.”
Phosphorus contamination of water was also an increasing issue in Denmark, added Mr Jensen. “Phosphorus content in Danish soils is generally high. While the loss from agricultural soils is low, other polluters have reduced their losses, so now agriculture is becoming the bigger polluter.”
To try to discourage the use of phosphorus in agriculture, a tax of E0.5/kg mineral P in feed additives was introduced last year. The synthetic alternative to mineral P (phytase) was also being promoted and could cut mineral P usage by 10-30%, he said.
What does this mean for the UK? “Things are certainly not going to get any easier, but it may not get as difficult as in Denmark,” said DEFRA’s Catchment Sensitive Farming delivery team manager, Patrice Mongelard.
Existing legislation such as Soil Protection Reviews, Nutrient Management Plans and Manure Management Plans provide a foundation for more detailed soil management, but diffuse water pollution from agriculture was still a significant challenge, he said.
“Catchment Sensitive Farming is here to stay and grow – it has a place under the measures of the Water Framework Directive.”