Kevin Ahearn manages Shinagh Dairy Farm, milking 250 cows in a spring calving system. The farm is part of the Farm Zero Climate (FZC) programme run by Biorbic, Carbery and Teagasc and is funded by Science Foundation Ireland (SFI). James Daunt is the Teagasc adviser to the farm.
Reducing chemical N use by 45%
All farmers are being asked to reduce their reliance on chemical nitrogen (N) and to switch from using CAN and straight urea to protected urea. Kevin was initially reluctant to engage with part one of this objective.
He was very nervous about cutting N by over 30% while at the same time maintaining grass grown on the farm . He was also mindful about not resorting to buying in additional feed to make up a potential shortfall in grass grown.
But after Kevin’s initial reservations, this has been a good news story.
Chemical N has been reduced by 45% or from 207kg N/ha in 2020 to 114kg N/ha in 2023. While at the same time, grass grown in 2023 is 12.2t DM/ha, down on 13.4t DM/ha grown in 2020. Growth was lower in 2022 at 11.7t DM/ha due to a severe drought.
Clover is the main driver of the reduction in chemical N use on this farm.
Kevin started by trying out clover in some paddocks and built confidence in it when he could see what it could do in terms of replacing artificial nitrogen.
He encouraged the clover by backing off applying N over the summer to these paddocks so that he could see what the clover could do. He matched neighbouring paddocks that were getting their full complement of artificial nitrogen.
The clover paddocks did get soiled water during the season. Initially these paddocks got nitrogen in spring for the first two rounds until mid-April.
In 2022, one paddock got no nitrogen for the full year and in 2023 this was increased to three paddocks. The performance of these paddocks has given Kevin the confidence to try this approach on more paddocks in 2024.
Clover has been increased on the farm through a combination of reseeding and top seeding clover into existing grass swards.
Kevin says top-seeding has about a 30% chance of being a success and very much depends on having the paddock well grazed off before applying the seed.
Damp weather afterwards ensures the seed germinates, and grazing the paddock two to three times at very low grass cover prevents the grass from shading out the tiny clover plants.
Full reseeding at a seeding rate of 5kg/ha (2kg/ac) of bare clover seed is a surer way of getting a successful result.
This method has been employed on the low-yielding grass paddocks as they require reseeding.
At this stage, 60% of the farm has a clover content of at least 15%. The silage ground that is not on the grazing block has been reseeded to a red clover and grass mixture.
This only gets slurry and artificial phosphorus (P) and potassium (K). It gets no chemical N. Kevin says it is matching the conventional silage paddocks that get a full allowance of chemical N in yield.
It has given three cuts of silage and one zero grazed cut this year. There is a final zero graze cut that is waiting until ground conditions allow it to be taken.
Below is a table showing the different amounts of chemical nitrogen applied to paddocks in 2023 and their grass yield. The high clover paddocks tend to be the most recently reseeded paddocks.
Kevin is soil sampling every two years and keeping the paddocks limed to achieve optimum soil pH.
Lime will be applied whenever there is an opportunity at any time of the year as waiting to get lime on in the autumn sometimes leads to lime not being spread as ground conditions may not be suitable for spreading.
Kevin is getting to the point that he hasn’t enough slurry on the farm. He is minding the slurry to apply to the red clover after each cut. This means holding slurry to apply after the September silage cut.
The farm has invested in extra tanks to make sure that valuable nutrients in the soiled water produced in November is available for spreading in the springtime.
All fertiliser on the Shinagh farm is spread by contractor. The contractor uses GPS equipment. There is no overspreading just to empty the spreader, as the accuracy of the GPS equipment ensures this does not happen.