Deirdre Hennessy warned listeners at the Irish Grassland Association’s dairy conference this week that if they do nothing, costs will increase.
She was speaking in relation to the requirement to reduce fertiliser use by 20% under the Farm to Fork strategy.
She explained that as the strategy is enforced, farmers who do not increase fertiliser use efficiency on their farms will either have to increase feed purchases or reduce stocking rates.
She stated that farmers need to over sow clover this spring to reduce nitrogen use in the summer and in years to come, as well as including clover in reseeds and spreading slurry using Low Emissions Slurry Spreading (LESS) equipment.
The Teagasc researcher commented that if you’re using LESS equipment to spread slurry, you should be applying less fertiliser, adding that where slurry is applied with LESS equipment in spring before summer, nitrogen fertiliser requirements can be reduced by 15-20kg/ha.
Hennessy added that there will be approximately 6kg of available N per 1,000 gallons of cattle slurry using a splash plate in the spring time, compared with 3kg in the summer. These figures increase to 9kg and 6kg respectively when a trailing shoe is used.
Another simple point made was that if you’re making surplus bales in every rotation, you can afford to cut mid-season nitrogen rates, and where grass measuring is being carried out, it will give confidence when cutting fertiliser rates.
White clover use, Hennessy pointed out, could reduce nitrogen application rates by up to 40%.
The industry target for nitrogen use efficiency (NUE) is 35%. The national average on Irish dairy farms is 25%.
Research on grass-only swards receiving 229kg N/ha reported a NUE rate of 40%, while swards with an average clover inclusion rate of 22% reported a NUE value of up to 58%.
This figure does not account for nitrogen fixed by the clover - it simply accounts for the reduction in fertiliser nitrogen applied and the increase in milk solids produced (78kg/ha more milk solids than the grass-only sward).
However, key to improving fertiliser use efficiency is maintaining soils at optimum soil fertility, so getting soil pH, phosphorus and potassium at optimum levels is essential in reducing nitrogen rates.