Reduce N Loss
5 min read
Nitrogen loss from your dairy farm negatively impacts both the environment and your efficiency. This page explains how excess nitrogen occurs mainly from the surplus intake in dairy cattle diets, and how it can contribute to pollution and greenhouse gases. You can reduce this nitrogen loss and improve your farm's performance by adjusting forages and N inputs, and ensuring less N ends up in urine. Additionally, manage your irrigation and cultivation strategies, and consider your farm's system to reduce nitrogen leaching. This way, you will help improve both your farm's financial and environmental performance.
Loss of nitrogen to the environment is driven by nitrogen inputs into the farm system, how efficiently they are used and how are they are recycled.
Nitrogen intake in most pasture-based diets is surplus to the requirements of dairy cattle. This surplus is excreted as urine (70-80%) and dung (20-30%). Nitrogen in the urine patch exceeds plant requirements, and thus is leached below the root zone or lost to the atmosphere as nitrous oxide gas (N2O).
The majority of N in the urine patch is initially in the form of urea which is rapidly hydrolysed (within 48 hours) to ammonium (NH4+). This ammonium is converted to nitrate (NO3-) by soil microbes through a process called nitrification. Nitrate is highly soluble and is the form of nitrogen plants can most readily use.
In the highly concentrated urine patch (equivalent to between 300-1000 kg N/ha), plants often can’t use it fast enough before it is carried below the root zone by soil drainage and thus lost via leaching events. The nitrate then ends up as a pollutant in ground and surface water. Leaching events are more common in high rainfall areas, under irrigation, as well as in free-draining soils.
The nitrification process also produces nitrous oxide gas (N2O), and another group of soil microbes can facilitate further N2O production from nitrate through a process called denitrification. N2O gas is 300 times more potent as a greenhouse gas than CO2. Its formation is more common in wet and compacted soils.
Research in the Forages for Reduced Nitrate Leaching programme (FRNL) has shown that catch crops, fodder beet and plantain can be used to reduce nitrate leaching.