The key areas of grassland management that are known to significantly reduce greenhouse gas emissions are fertiliser application and management of applications, grazing management, introduction of more diverse species into grassland including legumes and herbs, and correct use and application of farmyard manures and slurries
Effective, efficient use of artificial N fertilisers
Greenhouse gas emissions from synthetic fertilisers is a significant emissions source on grassland farms. 50% of emissions come from the production of the synthetic fertilisers and about 50% from the processes that take place in the soil after application. Estimates suggest that 10-30% of all applied nitrogen fertiliser is lost to the crop or grassland to which it is applied; use efficiency is influenced by application method and environmental conditions at the time of spreading. Make sure soil pH is above 6.5 if possible, soils are not compacted, that soil temperature is warm and rising and that soils are not not waterlogged. Do the basics well and you will get better yield response from your fertilisers and lower GHG emissions.
Reliance on Inorganic N fertiliser usage can be reduced through incorporating more legumes into swards. Establishing clover within temporary leys has additional benefits of higher protein forage and also a more diverse rooting system which can aid production in adverse climatic conditions. Typically grass clover swards containing around 30% clover by DM can fix around 120Kg – 180 Kg N /ha/ year. When they are in the sward, this is free nitrogen fertiliser!
As we are coming to appreciate that the nitrous oxide emissions associated with inorganic N fertilisers are a huge part of agriculture’s total emissions, improving N fertiliser use efficiency is critical. Saving 170kg N/ ha across 50ha will reduce emissions by around 58 tonnes CO2e which is more carbon than is sequestered annually in 10ha of broadleaf woodland.
Grazing Management
Grazing rotation is an excellent way to increase grass utilisation and reduce GHG emissions. Ensure there are adequate rest periods between grazing cycles to allow the sward to recover to optimise soil and plant health. Consider sub-dividing fields further to allow for more regular livestock movement. The long term effect of increasing rest periods and grazing taller grass is improved soil organic matter and soil structure. This will aid in reducing weed burden, lengthen the grazing season and improve resilience to flood and drought.
Including deeper rooting and more traditional species will increase above and below-ground biodiversity which may increase productivity alongside potential carbon capture and sequestration deeper into the soil profile. Ensure that grassland species composition supports production goals, soil type, soil pH and climatic conditions and consider overseeding where required.
Overseeding permanent pasture with improved diversity can provide a wide array of benefits. If 5 ha permanent pasture was over-seeded or re-seeded to create a herbal ley (consistent with SAM3 SFI) it could provide an additional -15.68 t CO2e of carbon removed per year. This will also build soil health and resilience by optimising the above ground canopy increasing the surface area of leaves for photosynthesis and supporting a greater below ground biodiversity responsible for cycling nutrients.
Accurate consideration of manures and slurries
Sampling and analysis of your farmyard manures and slurries will enable optimal accounting for the nutrients in them. Knowing what you are applying will enhance the accuracy of nutrient management planning and could reduce the requirement for synthetic N fertiliser. Consider the application method when applying organic manures to avoid nutrient losses and if possible cover muck heaps like silage heaps where possible to avoid dilution and runoff of nutrients.
