Reducing nutrient run-off
Alan Galbraith, Countryside Management Branch, Department of Agriculture and Rural Development (DARD)
A significant amount of nutrients, which originate from agriculture, are present in our waterways. These enter in numerous ways but one major source is through the direct run-off of slurry from fields. Typically in Northern Ireland a high proportion of slurry is applied during the months of January and February, despite the less than favourable weather and ground conditions that can prevail during this time. With modern slurry spreading equipment, generous applications of slurry can be applied even under very wet conditions. Applying when there is low nutrient uptake, wet soils and high rainfall often leads to a significant amount of slurry running off from fields into drains or directly into watercourses.
Risk of nitrogen (N) and phosphorus (P) run off
Research shows that the risk of contamination of watercourses from N occurs just after application. In contrast the risk from P contamination continues for a number of weeks afterwards if water is flowing in the drains. After each significant fall of rain, P in the drain water can be seen to rise and fall. Looking historically at the weather and ground conditions that prevail during the winter months it can therefore be deduced that very few days actually exist for safe application of slurry. Under the Nitrates Directive, farmers will be required to follow a number of measures that aim to control the loss of N and P to our waterways. The lack of suitable spreading dates during the winter period is one of the main arguments for a closed period.
| Control Measure | Benefit |
|---|---|
| Maximum application rate for organic N/ha | Restricting the stocking rate on farm to reduce the N and P loadin |
| Closed periods for application of slurry and fertiliser | Applying N and P when they can be used |
| Minimum storage period for slurry | To allow slurry to be applied when nutrients can be used and when soil conditions are favourable |
| Apply fertiliser N and P to crop requirements | To apply the correct amount of nutrients to minimise nutrient loss |
| Apply organic and inorganic fertilisers only when conditions are favourable | To allow the uptake of nutrients and to minimise run-off |
Improving efficiency
A closed period will demand the provision of additional storage on many farms. The cost of construction will vary according to requirements. However, part or all of the cost can be recouped by the improvement in the nutrient value of the slurry applied. For example, an above ground slurry store 'net of grant' has the potential to 'break even' in ten years due to the improved fertiliser value of slurry.
For further information on nutrient management in agriculture, contact Countryside Management Staff at your local DARD office.