How to reduce Nitrogen losses at farm level

Mary Roache, Teagasc Advisor Westport

The prohibited period when organic fertilisers are not allowed to be spread on Mayo farms came to an end on the 15^th January. Slurry and fertiliser spreading is prohibited over the winter in Ireland so as to comply with the European Union’s Nitrates Directive. The aim is to protect ground and surface water, including drinking water. The regulations also prohibit such application at any time of the year when the ground is frozen, waterlogged or heavy rain is forecast.

Losses typically occur where excess nitrogen fertiliser is applied above the crop requirement, especially when crop growth conditions are poor. When this happens, excess N in the form of nitrate in the soil not utilised by the grass or crop may be lost or leached to groundwater during heavy or prolonged rainfall. The reason for this is that nitrate does not bind tightly to soil and is prone to this type of loss through leaching in free draining soils.

Early and late nitrogen applications at farm level are usually the highest risk to water quality. Grass growth in the early months of the year (January/February) can vary. The response to N is generally low at this time of year which can result in poor recovery by the crop and increased risk of loss to water. Soil and weather conditions need to be monitored prior to applying N early in the early growing season.

Generally N losses are minimal during the active growing season due to reduced rainfall and the crops requirement is higher during this period. However care needs to be taken with the amount of chemical N applied as we enter autumn time, as this is typically a period of increased rainfall and decreasing crop growth. The closed spreading season is the period of the year with greatest risk of N loss to surface and groundwater, with up to 45% of the years N lost during this period.

Ways to minimise N leaching on your farm:

• Minimise leaching by using the right product (e.g. protected urea), in the right place at the right rate and time
• Use low emission equipment (LESS) when spreading slurry as this will allow for a reduction in the amount of chemical N required and it will also reduce ammonia losses to air
• Before spreading nitrogen or slurry, ensure there is no heavy rainfall forecast, soil temperature should be greater than 6 degrees and climbing, grass growth rates increasing and ground conditions trafficable
• Ensure soil fertility is optimum for lime, P and K. Follow your nutrient management plan (NMP). On moderate to highly stocked farms aim for P and K index 3
• Maintain buffer margins near water courses when spreading slurry in line with regulations (at least 5-10m)
• Soil sample regularly and update your NMP
• Ensure soil is not compacted, this will allow the root system of plants to access and absorb available nutrients readily

Nitrogen Use Efficiency (NUE)

Nitrogen Use Efficiency is a relatively new term. NUE calculates all N farm inputs vs the farm outputs (milk, meat, crops). N input sources on your farm typically come from chemical fertiliser, purchased feeds (concentrates and forage) and organic manure. Nitrogen use efficiency on livestock farms across Ireland is typically 20 -25% at present, in other words 20 - 25% of the N inputs on the farm are captured in farm products sold. The target is to increase NUE to 35% on grassland farms. Improving NUE has many opportunities not only to improve water quality by reducing nitrogen losses through leaching, but also by reducing costs and increasing profitability at farm level.