Reducing the organic nitrogen (N) stocking rate under the nitrates derogation to 220kg N/ha could have a detrimental impact on the environment, according to Teagasc.
The agriculture research and advisory body has published a new paper titled The Impact of Nitrogen Management Strategies within Grass Based Dairy Systems.
The paper said that reducing the maximum stocking rate under derogation from 250kg N/ha to 220kg N/ha may result in a move away from a pasture-based system in Ireland towards a “European model” of a forage maize or high concentrate feeding system, as some farmers may want to increase output while restricted with cow numbers.
According to Teagasc, international experience has shown that these high-input systems are more detrimental to the environment.
Under EU rules, which Ireland had to agree to in order to renew the derogation for this year, we are required, before June 30 this year, to submit a review of water conditions for last year. The review will contain the results of monitoring of nitrates concentrations of groundwater and surface waters.
It must also contain maps of areas that drain into water where monitoring shows the average value of nitrate concentration is above 50mg/L, or trends of nitrate concentration are increasing. These areas will be classed as polluted or at risk of pollution.
From January 1, 2024, farms located in these areas will see the maximum stocking rate under derogation cut to 220kg N/ha.
However, such a cut in derogation may have trade-offs that have a negative impact on the environment, according to Teagasc’s research.
The state agency said that a cut in derogation could also reduce grass utilisation on the most efficient Irish grassland farms.
Where stocking rate is not high enough to utilise the grass grown on a farm, it will result in lower grass utilisation, lower grass quality, and reduced animal performance.
According to the paper, N losses from Irish derogated grassland farms will reduce significantly over the coming years, due to significant reductions in chemical N application rates; changes to slurry management and soiled water storage; higher livestock N excretion rates plus banding; and an extended closed period for chemical fertiliser.
These measures will have the combined effect of reducing N surplus on Irish derogated grassland farms.
While it is possible that the reduction in chemical nitrogen use, as called for in the Food Vision Dairy Group report and the Nitrates Action Programme (NAP), could reduce grass production, Teagasc’s paper suggests that this could be “significantly” offset.
A reduction in grass production could be avoided through better soil fertility, increased use of clover, better grassland management practice, and improved nitrogen management.