How to reduce Nitrogen losses at farm level?

Mary Roache, Teagasc Advisor, Westport

Diffuse nitrogen (N) loss is a key pressure on water quality. Losses typically occur in ‘light’ free draining soils, which water can easily permeate through.   

Understanding how N losses occur is critical to mitigating against it. 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.

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 5.5 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 buffers near water courses when spreading slurry in line with regulation (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. By improving this figure, we can also reduce losses to water, the target is to increase NUE to 35% on grassland farms.

What can farmers do to improve NUE?

• Implementing the above measures
• Reduce use of chemical N through better use of slurry & use of clover
• Improving grass growth and utilisation
• Feeding less concentrates and/or lower protein concentrates, particularly during the grazing season

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.