Reducing the application rate of nitrogen (N) fertiliser by 25kg and 50kg N/ha could reduce farm profitability by 5% and 10% respectively, based on the results released in a new Teagasc study.

A new report called ‘Review of the Influence of Nitrogen Application Rate, Soil Type and Agroclimate Location on Grass Production, Feed Budget, Nitrogen Use Efficiency and Farm Profitability’ was published by Teagasc yesterday (Tuesday, November 24).

This was released on the same day as day one of the Teagasc Virtual Dairy Conference.

A key finding from the study found that the economic impact on a 40ha dairy farm of reducing N application rate by 25 and 50kg N/ha, in a fixed cow scenario when using 250kg N/ha, reduced farm profitability by €4,622 (5%) and €8,951 (10%), respectively.

The greenhouse gas marginal abatement costs are large when the reduced grass dry matter (DM) production is replaced with imported feed onto the farm, the report noted.

Meanwhile, reducing N application rate by 20% on suckler beef farms reduced gross margin per hectare by 7% and net margin by 12%.

Reducing N application rate by 22% on lowland sheep farms reduced lamb output per hectare by 15% and net margin per hectare by 16%.

However, incorporating white clover into existing pastures and use of NUE (nitrogen use efficiency) technologies has the potential to reduce these negative economic impacts, it was added.

On a fodder note, reducing N application rate from 250 to 200kg/ha at a stocking rate of 2.5 cows/ha reduced the feed available on the farm from a surplus of 119kg DM/ha to a deficit of 433kg DM/ha. No cognisance was taken on the effect of reduced N fertilisation on grass chemical composition, it was added.

A number of other key findings were also highlighted in the report, including environmental research and technology study.


It was noted that a review of six large-scale dairy cow grazing experiments in the Republic of Ireland predicted that the rate of N which gave the maximum percentage change in stock carrying capacity was approximately 300kg N/ha on both freely and imperfectly drained soils.

N surplus increases with increased N fertiliser application and increased stocking rate, which increases the risk of N loss.

However, water quality responses in groundwater and surface water are influenced by both static (e.g. soil, subsoil and bedrock type) and dynamic factors (e.g. climate, soil moisture deficit, depth to water table), which are spatially and temporally variable across the farming landscape.

There is a variable time lag – ranging months to decades – between N surplus losses and changes to water quality and this must always be acknowledged when considering the efficacy of programmes of measures.


On a more positive note, greater use of low emission slurry spreading technology, protected urea, increased soil fertility (including soil pH) and greater precision in grazing management have the potential to reduce N required for a given level of grass growth which would reduce N emissions.

Research has shown that incorporating white clover into grassland reduces requirement for chemical N by up to 100kg N/ha and increases animal performance.

However, the adoption of this technology at farm level has been very limited; it will require a number of years before there are sufficient uptake to replace significant levels of chemical N fertiliser. A considerable knowledge transfer and a continued research programme are required to get significant adoption.

Grass-based systems are focused on maximising grass production and utilisation and minimising the amount of feed imported onto the farm. This is both more profitable and more environmentally sustainable.

A move to lower grass production “carries the risk of greater importation of feed onto the farm which will lead to reduced profitability and a deterioration in environmental sustainability as has been demonstrated around the world”, the report said.