38% reduction in nitrogen on Laois farm

With clover on almost 90% of the farm, James Barber is in a position that many farmers aspire to be in. James is milking 110 cows on a 114ac farm between Cullahill and Rathdowney in Co Laois. The heifers are contract-reared and there are no outblocks so the only stock on the farm are the cows.

The farm was traditionally in tillage and soil type can only be classed as excellent – brown earth over limestone.

The whole farm has been reseeded over the last 10 or 11 years. James has been part of the Teagasc on-farm monoculture grass study and is now part of the Teagasc Clover 150 project and a farm walk was held there last week for farmers in the programme.

A clover assessment is carried out three times per year by programme co-ordinator Caitlin Looney. On average in 2022, 25% of the farm had a clover content of greater than 20% in the sward with another 18% of the farm with a clover content of between 18% and 20% clover.

So far this year, the farm has grown 10.9t DM/ha from 149kg chemical N/ha.

Last year, James applied 241kg N/ha, so there has been a 38% reduction in chemical nitrogen this year.

We’ve never had a drought so bad or so late as this year

While that is a substantial difference in chemical nitrogen, the two years were by no means the same and 2022 was a challenging year for grass on the farm, with a severe grass shortage in August and September due to soil moisture deficits.

“We’ve never had a drought so bad or so late as this year.

“We let the average farm cover run down and then went in with feed. We usually buy in 10 acres of maize every year and we had one quarter of this left over from last year, so we fed that in August along with 30 round bales of silage.

“We started eating into our winter silage in September, so we ended up buying 200 round bales of hay for the winter,” James says.

Despite the dry spell, the farm should still grow around 13.5t DM/ha this year, which is similar to last year but with far less chemical nitrogen.

Distribution

When looking at the distribution of chemical nitrogen across the farm, there is little difference in chemical N between the high clover and low clover fields with those less than 5% clover getting 143kg N/ha and those with more than 20% clover getting 149kg N/ha.

The low clover fields have grown 9.8t DM/ha to date, while the high clover fields have grown 11.2t DM/ha to date.

It could be argued that if the chemical nitrogen was applied in a more targeted way, then the farm could grow more grass.

For example, if 50kg or 60kg N/ha was taken off the high clover paddocks and spread on low-clover paddocks or paddocks with no clover, you would expect that these paddocks would grow more.

The bigger question is, would the high-clover paddocks grow the same if they got around 100kg N/ha rather than the 149kg N/ha they got this year?

This is probably the next step for farmers who have a high proportion of clover on the farm.

The challenge with this approach is that it gets harder to increase the clover content on these low and no-clover fields because, as we know, it’s very hard to get clover established when there are high rates of nitrogen being spread.

Grazing infrastructure

Grazing infrastructure on the Barber farm is excellent with super roadways, paddock access and water troughs throughout the farm.

Average farm cover is currently 1,046kg/ha, growth was 29kg/day last week and the herd was producing 1.6kg MS/cow on 2kg of meal. James says he was feeding silage up to two weeks ago to build covers.

He has 700kg of meal fed to date and the herd will produce over 500kg MS/cow again this year.

The target is to close the farm with an average farm cover of 650kg/ha. The first closed paddock has a cover of 600kg back on it already, so James says he will probably be grazing this again, but a decision won’t be made until the end of November.

Bloat has not been a problem on the Barber farm but James is making a big effort to avoid it. When cows are grazing high-clover fields, James uses a ‘breakfast break’, which is a small allocation of the paddock that will have enough grass for two hours or so.

When this section is fully grazed, he’ll let them into the whole field. Cows are currently on 12-hour breaks and James is still giving a breakfast break each morning.

The thinking behind this small break of grass is that the area to the cows will be restricted, meaning cows can’t gorge themselves on clover and will be forced to eat down into stem, which has higher fibre content.

Summer and autumn seem to be the highest risk periods

A survey of 24 farmers in the Clover 150 group showed that half the group have experienced bloat in the past, with six farmers experiencing bloat this year. Summer and autumn seem to be the highest risk periods.

There are usually a number of factors that lead to bloat, but hungry cows going into a high clover field is a big risk factor. So too is grazing in dry weather after a strong period of growth post drought, lush green grass and grazing reseeds. Most bloat occurs on covers of between 1,000kg and 1,500kg.

The Teagasc advice to avoid bloat is to try and be consistent with swards as problems tend to happen when cows go from grass-only swards to grass and clover swards.

Use a strip wire to control grass allocations. Use bloat oil at high-risk times and make sure all cows enter a high-clover paddock at the one time. This means holding cows back after milking and letting them all out together. This is to ensure that the first cows out of the parlour don’t gorge themselves on clover. Extra fibre in the diet during high-risk times, such as straw or dry silage, can reduce the risk of bloat.

John O’Loughlin from Grassland Agro was speaking about background nitrogen and how it can contribute to grass growth.

He says that there are three pillars to improving soil health; the first is chemical fertiliser, such as N, P and K. Second is biological activity such as worms and bugs and the final one is soil structure.

“We need all three in order to grow high levels of grass per hectare. High chemical nitrogen rates erode soil biology, so back when nitrogen was cheap and farmers were able to spread plenty of it, it could have been masking an underlying soil health problem.

“Now that nitrogen is expensive and limited, farmers need to focus more on soil biology and soil structure in order to release more background nitrogen,” John says.

He says that every tonne of grass dry matter requires 30kg of nitrogen to grow. So for a field to grow 15t DM/ha, the grass needs 450kg N/ha.

He says that if 150kg N/ha was applied in the form of chemical nitrogen and 120kg to 130kg N/ha was got from clover, 170kg to 180kg is required to come from the soil itself through mineralisation of labile nitrogen.

“Over the course of a growing season mineralisation will follow the grass growth curve and is determined by soil temperature and length of day. Soil structure has a huge impact on the availability of nutrients in the soil.

“On a soil structure score of one to four, with one being good, most Irish dairy farms have a score of 2.7 so there is room for improvement,” John says.