Nitrates Directive and Nitrogen Efficiency

Alan Galbraith, Countryside Management Branch, Department of Agriculture and Rural Development (DARD)

One key aspect of the Nitrates Directive is to encourage farmers to make best use of the nutrients contained within their slurries. Currently in Northern Ireland approximately only one quarter of the nitrogen in manures is being taken up by the crop. This low level of efficiency represents a huge loss in financial terms to the agricultural industry and has contributed to the deterioration of our water quality.

What can be achieved?

Some European countries, such as Denmark, are achieving a very high level of nitrogen (N) efficiency. In Northern Ireland this very high level of efficiency cannot be achieved because of limitations due to soil type and farm practices. Nevertheless, N efficiency will have to be increased and two changes can be made that will improve nitrogen efficiency:

·Minimising the potential for nitrogen to leach out of the soil.
·Minimising the loss of nitrogen to the atmosphere.

Minimising Leaching

Currently slurries are spread all year round including the non-growing season. The Action Plan under the Nitrates Directive will prohibit application of slurries during the winter months. This will result in a high proportion of slurries being applied in spring, which is the most beneficial time for grass and crop growth. This will minimise the potential for nitrogen leaching. Also, by having the required minimum storage period of 26 weeks for pig and poultry enterprises, and 22 weeks for other enterprises, slurry can be stored and then applied when most benefit can be derived from it. This will reduce the risk of overflowing tanks and spreading when ground conditions are unfavourable.

Preventing Atmospheric losses

Slurry contains up to 50 percent of its nitrogen in the form of ammonium which is readily lost as ammonia. The amount of nitrogen contained in the slurry and available for swards to use will depend on the type of housing, slurry facilities and slurry spreading methods. The way that slurry is managed and the length of time and the surface area of the slurry in contact with the atmosphere will determine the amount of nitrogen loss.

·Large shallow tanks tend to have higher losses than smaller deeper tanks with above ground slurry stores having the least potential for losses.
·Allowing cattle slurries to form a crust will reduce losses. Above ground slurry stores can be covered.
·The largest loss of nitrogen occurs from the spreading of livestock slurry. Spreading techniques such as trailing hose, trailing shoe or injection methods, significantly decrease the surface area of the spread slurry exposed to air and greatly reduce the loss of nitrogen to the atmosphere making more nitrogen available for plant growth.

Improving nitrogen efficiency by complying with the Nitrates Directive will improve nutrient use in manures and reduce the amount of fertiliser required. Farmers, who make allowance for the nitrogen applied in slurries when estimating the fertiliser nitrogen requirements for grass or crops, will bring cost savings to the farm, and benefits to the environment