Nitrogen Fertilisers - Improving Efficiency and Saving Money
Becoming more efficient in the application of nitrogen fertilisers on farms and avoiding nitrogen losses has direct financial benefits for farmers, and reduces nitrous oxide emissions and nitrate runoff into waterways. Nitrous oxide is emitted from soils, nitrogen rich fertilisers as well as from stock effluent.
Nitrogen is critical to plant growth and reproduction. The demands of production agriculture require higher levels of nitrogen than are normally found in native soils. This situation is often managed through the addition of nitrogen fertilisers.
Farmers can save money, boost production and reduce nitrous oxide losses by carefully planning and implementing best management practices with regard to the rate, source, timing and placement of fertilisers.
What is Nitrous oxide
Nitrogen-based fertilisers and livestock waste (urine and dung) are the key sources of nitrous oxide emissions on farms. Nitrous oxide is an extremely potent greenhouse gas (about 310 times that of carbon dioxide) that remains in the atmosphere for over 100 years. Nitrous oxide is most likely released in warm, waterlogged soils where there is excess nitrogen present
Options of managing nitrogen fertilisers and emissions
Research has estimated that between 40%1 and 60%2 of nitrogen inputs into cropping and grazing systems, respectively, is lost to the environment and never completes the cycle into agricultural product. The percentage of nitrogen inputs lost is fairly consistent across different rainfall zones, but the process and quantity of what is lost differs.
The following points are examples of actions that farm businesses can take to improve their emissions performance on-farm with respect to nitrogen fertilisers.
- Determine and improve plant access to nitrogen by improving soil health and nutrient status – see previous section on 'Soils'. Pouring additional nitrogen inputs onto soils that have inherent limitations to crop growth is unlikely to result in financial gain.
- Avoid application of nitrogen fertilisers (especially nitrate) to waterlogged soils.
- Place fertiliser below the soil surface where possible to limit ammonia volatilisation (especially on alkaline soils).
- Match nitrogen supply to crop or pasture demand by:
- using soil or plant testing to assess plant available nitrogen supply and decide on the quantity of fertiliser to apply based on a calculation of target yield and crop nitrogen requirement over the growing season.
- if available, using appropriate, industry-relevant decision support tools (e.g. Yield Prophet in Grains) and seasonal forecasts for more timely and calibrated fertiliser decision support – knowledge of moisture status and soil nitrogen reserve and supply need to be taken into account.
- avoiding high application rates of nitrogen in any single application (i.e. never exceed recommended rates, split applications are more effective and adjust rates according to rainfall).
- Time fertiliser application to minimise nitrogen loss via denitrification or volatilisation
- apply nitrogen fertiliser when the crop needs it rather than earlier in the season (when there is a greater probability of losses), as crop/pasture demand for nitrogen is usually greatest during early spring.
- avoid tillage under wet conditions. Large amounts of nitrogen can build up in the soil (via mineralisation) following a pasture legume (or pulse crop) phase and this nitrogen is especially susceptible to losses following tillage under wet conditions.
- Choose the best source of nitrogen:
- in the wet season urea and DAP will lose less nitrate and nitrous oxide than nitrate based fertilisers.
- where possible use an inhibitor coated fertiliser; in summer to reduce ammonia loss and in winter to reduce nitrous oxide and nitrate leaching losses.
- Consider how you might incorporate fertiliser at the top of raised beds or ridges to avoid wet areas.
- Estimate the methane and nitrous oxide emissions on your farm using a greenhouse gas accounting tool appropriate for your type of enterprise.
1Stevenson, Frank J. 1982, Nitrogen in agricultural soils / Frank J. Stevenson, editor American Society of Agronomy, Madison, Wis.
2Whitehead, David Charles. 1970, The role of nitrogen in grassland productivity : a review of information from temperate regions / by D.C. Whitehead Commonwealth Agricultural Bureaux, Farnham Royal, Bucks.
Other useful links
- Best management practices for nitrogen on pastures
- Nitrous Oxide Research Program
- Greenhouse in Agriculture – research and best management practices
- Video presentation by PICCC Director Richard Eckard on nitrous oxide in crops and pastures.
- Fertilising dairy pastures: nitrogenous fertilisers
- Dairy Australia Reducing Nitrous Oxide