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New Nitrogen report published at Teagasc Virtual Dairy Conference


A new report: ‘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 at this year’s Teagasc Virtual Dairy Conference in November. See it here again below

The expansion in the dairy industry in recent years has resulted in an increase in land area allocated to dairy farming. At farm-gate level the expansion has resulted in an increase in nitrogen (N) surplus, increases in N use efficiency and lower emissions of N per unit of production.

Review of grazing experiments

A review of six large-scale dairy cow grazing experiments predicted that the rate of N fertiliser application which gave the greatest percentage change in stock carrying capacity was approximately 300 kg N/ha on both freely and imperfectly drained soils. A clay loam soil produced approximately 1,000 kg dry matter (DM)/ha more grass than a sandy loam soil, while the agroclimatic conditions at Moorepark produced 270 kg DM/ha more grass than at Ballyhaise. Soil type and location had only a small impact on response to N fertiliser application rate. Reducing N application rate from 250 to 200 kg/ha, at a stocking rate of 2.5 cows/ha reduced the feed available on the farm from a surplus to a deficit. No account was taken on the effect of reduced N fertilisation on grass chemical composition. Surplus nitrogen increases with increased N fertilizer 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 factors (e.g. soil, subsoil and bedrock type) and dynamic factors (e.g. climate, soil moisture deficit, depth to water table), which are variable across the farming landscape. There is a variable time lag, from months to decades between the losses of surplus N and changes to water quality and this must always be acknowledged when considering the efficacy of programmes of measures.

Reducing N – the economic impact

The economic impact on a 40 ha dairy farm of reducing N application rate by 25 and 50 kg N/ha in a fixed cow scenario when using a 250 kg N/ha fertiliser application rate reduced farm profitability by €4,622 (5%) and €8,951 (10%), respectively. The GHG marginal abatement costs are large when the reduced grass DM production is replaced with imported feed onto the farm. Incorporating white clover into existing pastures and use of N use efficiency technologies has the potential to reduce these negative economic impacts. 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%.

Technology strategies help alleviate reductions

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 100 kg N/ha and increases animal performance. The adoption of this technology by farmers at farm level has been very limited. It will require a number of years before there is satisfactory uptake to replace significant levels of chemical N fertilizer. A considerable knowledge transfer and a continued research programme are required to get significant farmer uptake. Grass-based systems are focused on maximising grass production and utilisation while 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.

Report Editors are: Pat Dillon, Laurence Shalloo, Elodie Ruelle and Owen Fenton

See the full report at https://teagasc.ie/publications/2020/review-of-the-influence-of-chemical-nitrogen-application-rate-soil-type-and-agroclimate-location-on.php