Steps to Reduce Chemical Nitrogen Usage on Farms

By Shauna Fitzmaurice, B&T Drystock Advisor, Teagasc Galway/Clare

The Government’s Climate Action Plan 2021 has set out a target to reduce greenhouse gas emissions from agriculture in Ireland by 22-30% by 2030. One measure that has been highlighted as a method to achieve this target is to reduce chemical nitrogen fertiliser use on Irish farms by up to 20% by 2030. Not only will this reduce the level of greenhouse gas emissions from Irish agriculture but it can also lead to an improvement in farm profitability when measures such as improving soil fertility, optimising use of organic manures and reducing waste are implemented.

Actions to reduce chemical N fertiliser use:

1. Know how much chemical N fertiliser is currently being spread on your farm - Tools such as the PastureBase Ireland app can help you to record the quantity of fertiliser spread on each paddock throughout the year.
2. Know the soil fertility status of your farm - Take soil samples every two to three years and complete a nutrient management plan based on this. This will allow you to target fertiliser use where the best results can be achieved. Soil sample results allow you to identify paddocks that require lime, identify fields that are high and low in P and K fertility and ensure that nutrient demanding crops e.g. silage receive enough nutrients to promote growth and replace offtakes. Ideally soils should be pH 6.3+ and phosphorus (P) and potassium (K) Index 3.
3. Spread sufficient lime on the farm - Lime improves soil pH which in turn releases up to 80kg N/ha/year and unlocks soil P and K leading to increases in annual grass production.
   
   

   Crop type	Target soil pH
   Grassland (mineral soils) grass only swards	≥6.3
   Grassland (mineral soils) with clover	6.8 to 7.0
   Grassland (peat soils)	5.5 to 5.8
   Cereals	≥6.5
   Beet/beans/peas/oilseed/maize	6.8 to 7.0
   High molybdenum (Mo) soils	6.0 to 6.2

4. Optimise organic fertiliser N usage - The use of low-emission slurry spreading (LESS) equipment such as a dribble bar or trailing shoe will increase the N content of the slurry by three units/1000 gallons in comparison to using a splash plate. Slurry should be spread in spring time to avail of higher N availability in comparison to spreading in summer time. Maximise the use of slurry on silage ground. The majority of silage paddocks P and K requirements can be fulfilled by spreading 3000 gallons of slurry/acre. The benefit of using organic manures on the farm will only be realised if chemical N fertiliser rates are reduced to allow for N applied in slurry.
5. Incorporate clover into grassland swards - The incorporation of white clover into grassland will reduce the level of chemical N fertiliser required on the farm by up to 100kg/ha. The target on farms is for 100% of paddocks to have 20-25% white clover in the sward.
6. Measure grass yield and use data on growth rates to make informed decisions - Walk your farm weekly and measure how much grass is available. Use this information to identify surpluses and deficits in grass supply and adjust N fertiliser applications accordingly. If paddocks are not performing as well as expected investigate the reason why rather than increasing chemical N application straight away.
7. Avoid wasting fertiliser on your farm - Calibrate your fertiliser/slurry spreader to ensure accurate application levels. Adhere to buffer zones to prevent runoff into watercourses and protect against water pollution. Avoid spreading too close to hedgerows, roadways or gateways. Use GPS technology to improve the accuracy of fertiliser spreading.
8. Do a fodder budget - Be aware of how much feed is required on your farm for the winter and include a reserve of 20% extra for difficult years. Match fertiliser N application rates to the demand for fodder. PastureBase Ireland can be used to record the fodder budget for your farm.
9. Know the four Rs:
• Right product – Select the correct products to deliver a balanced supply of N, P, K and S.
• Right rate – Assess soil supply and crop requirements and apply sufficient nutrients for high crop yields.
• Right time – Apply nutrients when crops can utilise them efficiently.
• Right place – Ensure nutrients are applied accurately and evenly.