The scene was set fairly quickly by Jack Nolan at the Teagasc dairy conference last week. Nolan, a senior inspector with the Department of Agriculture, challenged dairy farmers to try to reduce fertiliser usage by a half bag/acre of urea, or one bag/acre of CAN next year;

“We need to start making a difference [to water quality] straight away, not from two years’ time but from now on.”

He said that for farmers to keep farming and to keep producing food wanted by the consumer farmers need to change their practices around fertiliser use. He stressed the importance of improving soil fertility, liming and better timing of slurry applications as key steps for reducing nitrogen usage.

Teagasc researcher Laurence Shalloo said that there are 40% more dairy cows in Ireland now than there were in 2010 and that 40% of these extra cows have been facilitated by increased stocking rate. In other words, about 200,000 of the extra cows in Ireland are on land that was already being farmed by dairy farmers in 2010.

He said that dairy farmers have become more efficient in the last decade, with grass utilised per hectare a key metric of profitability, increasing by 25% or 1.3tDM/ha;

“Of that 25% increase in utilisation the majority is coming from efficiency – better grazing management, rather than from nitrogen usage. There is this perception that all the expansion has come from increased nitrogen – not at all. About 70% of the increase has come from better efficiency at farm level,” Shalloo said.

Response

Elodie Ruelle, a researcher based in Moorepark, outlined some of the expected responses from fertiliser on different soil types and at different times of the year. A response to chemical nitrogen is the extra grass growth that was achieved from applying that fertiliser, over and above what grass would be grown by naturally present soil organic nitrogen.

The annual response from nitrogen fertiliser is around 20kg of grass for every 1kg of chemical nitrogen applied per hectare on free-draining soils and 19kg of grass for every 1kg N/ha applied on heavier soils. These responses are based on applying between 100kg and 150kg N/ha per year. As the annual chemical nitrogen application increases, the response rate decreases as there is more nitrogen already in the soil system. The response when applying between 200kg and 250kg N/ha per year is 16kg grass for every 1kg N/ha, which Ruelle said is still a very good response.

“There is a difference in response between the seasons. The response in summer will be way higher than in spring and autumn. The response in summer is higher because temperature is optimal and daylight hours are longest. While this is the case, we also have to remember that the response in spring and autumn is still fairly good and that this is a time when that extra grass growth is highly valuable,” Ruelle said.

Implications

Laurence Shalloo outlined the findings of a new Teagasc report on nitrogen usage, which looked at the financial implications of reducing chemical nitrogen usage on dairy farms. The findings suggest that where chemical nitrogen is reduced by 20%, farm profit is likely to reduce by 10% as many of the fixed costs won’t be changed even if cow numbers decrease. A 10% reduction in fertiliser usage resulted in a 5% reduction in profit under the same scenario.

Eoin Fenton, a Teagasc researcher from Johnstown Castle, looked at nitrogen from an environmental perspective. He said that surplus nitrogen is lost nitrogen and it can be lost to the atmosphere or to water. He made the important point that ground water and rivers are connected, so what happens to groundwater affects river water quality and these rivers then all flow to estuaries.

“We really have to be cognisant about where our nitrates end up and that is in our estuaries,” Fenton said.

He said that what happens above ground can take months or years to have an effect on water quality.

“There is a storage of nitrogen in our soils, so what we’ve done in the past affects water quality now and what we’re doing now on the farm will affect water quality into the future. So we have to manage our expectations. It may take months or years for the nitrate concentrations to have an effect on the river or the estuary. The big point here is that in our free-draining areas that takes a short amount of time, but it takes longer for moderately drained soils and much longer for poorly drained soils.”

When asked where she would reduce chemical nitrogen usage, Ruelle said there is very little capacity to reduce chemical nitrogen as the extra growth was required in all the seasons.

Research

The researchers spoke about ways to increase nitrogen use efficiency (NUE). This is the amount of nitrogen that is applied and used for grass growth as opposed to nitrogen applied and lost to the atmosphere or to ground water. Laurence Shalloo said the gains made over the last 10 years are a signal that future gains can be made.

“Probably the most important factor affecting NUE is grassland management. Looking at the National Farm Survey, we estimate that the average farm is growing approximately 10t/ha of grass and in terms of PastureBase we know that the average is 13t/ha of grass so there is a 3t/ha difference there for a similar level of nitrogen,” Shalloo said.

He went on to say that better grassland management means a greater focus on pre-grazing yields, post-grazing residuals and measuring grass on a regular basis along with reseeding and soil fertility. He said clover was a big factor and that research has consistently shown high clover swards to deliver between 1.5t and 1.6t DM/ha extra pasture.

“Obviously, that’s not straightforward nor is it simple and there’s a serious amount of management needed to get it established and to stay in the sward but the benefits have been well proven at this stage.”

The other things Shalloo mentioned to increase NUE were to use more slurry in springtime and to apply slurry with low emission equipment. He said farmers can grow another 300kg to 400kg more grass per hectare by using more slurry in spring and using low-emission slurry spreading.

Stocking rates

On the question of grazing platform stocking rates, Laurence Shalloo said the Teagasc view is that 2.7 cows/ha is the optimum stocking rate.

“To have a stocking rate of 2.7 cows/ha you have to be growing around 15t of grass per hectare and when we look at PastureBase data or any data there are very few farmers that are in that zone. The stocking rate should be directly related to what the farm is growing and we shouldn’t be driving up the stocking rate if we’re not growing the grass because the feed for those additional cows is coming from outside and that’s adding cost to the system.

“From an economic point of view, we have looked at this a number of times in different studies with high stocking rates and bringing in feed. When you include all the costs including labour, those stocking rates are less profitable than keeping the stocking rate optimum on the platform. So where does the balance lie? For me, the balance is bringing in, at a maximum, 50% of your winter feed from outside.” Shalloo used the example of a farm growing 15t/ha. If all the winter feed was grown on the platform the stocking rate could be 2.8 cows/ha but where 50% of the winter feed was being brought in, the stocking rate could increase to 3.3 cows/ha.

“Once you go beyond that you are having a serious, negative financial impact on your business. That is when you include all costs. If you don’t include your own labour with the extra cows and work in that system, you might see some sort of a return, but that is a classic example of running faster to stand still,” Shalloo said.

Comment

It’s clear from listening to the researchers that grassland management is key to improving nitrogen use efficiency, yet there is no environmental “reward” for farmers who are good at managing grass. The same can be said for those that adopt the other measures spoken about such as high clover content, LESS, protected urea, additional slurry storage, good soil fertility, reduced chemical nitrogen, low protein feeds and low levels of bought in feed.

Why are all farmers and why are all hectares being treated the same under the Nitrates Directive? There needs to be a greater incentive and reward for changing practice.

The more I think about it, the more I see the merits in a farm system model like they have in New Zealand where each farm is treated differently and the nutrient surplus and greenhouse gas emissions are calculated per farm.