The expansion of the Irish dairy sector in recent years has increased the land area allocated to dairy farming.
With many farms converting to dairy or existing dairy farms expanding, it has lead to an increase in the levels of chemical nitrogen (N) being spread to encourage increased yields of grass growth.
Following a recent grazing experiment of N fertiliser application on six large-scale dairy cow herds – it was predicted that the rate applied which gave the greatest percentage change in stock carrying capacity was approximately 300kg N/ha on both freely and imperfectly drained soils.
This study was conducted by Teagasc, as part of the ‘Review of the influence of nitrogen application rate, soil type and agroclimate location on grass production, feed budget, nitrogen use efficiency and farm profitability’.
The research illustrated that a reduction in N application rates from 250kg/ha to 200kg/ha, at a stocking rate of 2.5 cows/ha, reduced the feed available on the farm from a surplus to a deficit.
Economic impact
The reported study also examined the economic impact on a 40ha dairy farm.
The results found that by reducing the N application rate by 25kg N/ha and 50kg N/ha in a fixed cow scenario when using a 250kg N/ha fertiliser application rate – farm profitability was reduced by €4,622 (5%) and €8,951 (10%), respectively.
Reducing N application rate by 20% on suckler beef farms reduced gross margins per hectare by 7% and net margins by 12%.
On lowland sheep farms, reducing N application rate by 22% reduced lamb output per hectare by 15% and net margin per hectare by 16%, according to Teagasc research.
The report concluded by stating the incorporation of white clover into existing pastures and use of N use efficiency technologies has the potential to reduce these negative economic impacts.