Pros and cons in Zero N red clover project

Initial data coming from farms taking part in the AgriSearch-led ZeroNsile project shows it is possible to grow good crops of red clover-based silage in NI, but there are a number of weather-dependent challenges around getting it established and ensiled.

The ZeroNsile project started in 2023, with the aim to demonstrate the feasibility of producing silage without the use of chemical nitrogen (N) fertiliser. The farmers involved were encouraged to grow up to 5ha of red clover, as well as a comparable field of ryegrass.

The red clover swards were not a monoculture, with 3kg to 4.5kg/acre of red clover included in a mix alongside 8kg to 10.5kg of grass seed. There was also approximately 1kg of white clover added to help ensure some legumes persisted when red clover dies out.

Given a wet 2023, some farmers did not get red clover established at all. For those who did, taking bales off later in the season was a salvage operation.

2024 yields

Last year was significantly better, however, poor spring growth negatively impacted yields across all farms.

“It has been a couple of challenging years so far,” AFBI forage scientist, Dr David Patterson told attendees at an AgriSearch online event last Wednesday night.

Data from project farms in 2024 show very similar first- and second-cut yields across red clover and grass-only swards, although with good growing conditions late in season, third-cut yields from red clover swards were significantly ahead of grass-only counterparts.

Overall, yields across all swards were down on what would normally be expected in a typical year.

Quality

The quality of the herbage was also assessed pre-cutting and showed that dry matter tends to be lower in red clover swards, as well as energy and digestibility. There was no significant difference found in crude protein, although the protein levels were all much higher in third cuts.

“The crude proteins reflect the poor year – you need sunlight to build protein,” said Patterson.

Despite results suggesting that red clover is of slightly lower quality, the consensus is that actual animal performance is improved when red clover silage is fed. Potentially that is due to higher intakes and also because nutrients in red clover are better able to by-pass the rumen and be taken up by the animal, suggested Patterson.

With red clover able to fix atmospheric N, there is zero requirement for chemical N fertiliser, however, the crop still needs phosphorus (P) and potassium (K). Where a field is at Index 2+ for both nutrients, this total annual crop requirement is 90kg P and 200kg K/ha.

If 3,000 gallons of slurry is applied per acre before first cut, followed by 1,000 gallons and 2,500 gallons before second and third cuts, this will supply approximately 87kg P and 167kg K. So while the P requirement is met, there is a shortfall in K.

“You maybe should add a single application of straight K at some stage of the season,” suggested Dr Patterson.

The AgriSearch event heard from two Tyrone dairy farmers involved in the ZeroNsile project.

Dromore farmer Frank McDonnell got his red clover sward established on 26 June 2024, with the field baled on 2 September 2024.

He said one issue was finding someone in the Dromore area with a suitable seed drill.

He also told farmers not to stack the bales of red clover silage.

“Stack them on their end and don’t go higher than one,” said Frank.

The second farmer was Andrew Crawford from Beragh. His red clover sward and grass-only control, was established in late July and early August of 2023.

In 2024, three cuts were taken off both swards, however, “neither did great” said Andrew.

The red clover did yield 9.45t dry matter per hectare (DM/ha) with the grass-only control growing 8.37t.

“The control got over 270kg N/ha which works out at £100 per acre, but it grew over 1t DM less,” he said.

While that is a major positive, there are negatives. Andrew said the red clover has become patchy, which he believes is because it was mowed too tight.The red clover growing point is just above the surface and if it is damaged, the plant will die. As a result, the advice is to mow at around 4-5cm and avoid “scalping” the ground.

However, in practice, with a contractor coming in with triple mowers and under pressure due to a tight weather window, the message around cutting height might get lost.

“Red clover complicates the system as a whole, particularly in a challenging year,” said Andrew.

Red clover should be drilled into a fine, firm and fertile seed bed, ideally between mid-April and mid-May, advised Dr Patterson.

The existing sward should be burned off and there must be some degree of cultivation, but it doesn’t have to be ploughed, he said.

The red clover must not be buried too deeply (below 10cm) and it is vital to have pH at around 6.5.

Once established, one of the main issues is weed control. While there is now a new clover-safe spray on the NI market (ProClova), it can only be used on red clover in its second year. “There is not any great chemical option for the first year of red clover,” said Patterson.

As a result, it is important to get weeds under control in the previous year, he added.

Ensiling

The other main challenge is at ensiling and making sure the crop is not cut too low (below 4 to 5cm) and the red clover leaves (which contain nutrients) are not damaged.

“Tedd once and do it gently, straight after the mower. It is the same with the rake – make sure it is not done at breakneck speed,” advised the AFBI scientist.

Farm management at Greenmount is now moving into its third year of a four year project to get white clover established in grazing swards across dairy and lowland beef and sheep farms at the college.

Providing an update, CAFRE forage technologist Robert Patterson said the aim was to get N input down from 250kg/ha to well below 150kg on the dairy platform and on the beef and sheep farm, down from around 150kg to a maximum of 80kg N/ha.

A number of techniques have been used. The most reliable has been to spray off the sward, followed by cultivation and sowing, but given the time the sward is out of production, it is “a hard drain on the grazing platform”, said Patterson.

As a result, most paddocks have been overseeded straight after grazing or a cut of bales. This is best done between mid-April and mid-May, thereby avoiding a potential moisture deficit in June.

Post-sowing management is key to getting the clover established.

It is necessary to shorten the rotation length, while no N fertiliser has been applied at sowing or after the first grazing to help prevent grass shading out new clover plants. After that, a half rate of around 12kg N/ha of N (approximately half a bag per acre) has been used.

“The best case scenario is that there is no N – but it is a balancing act as we have a herd of cows to feed,” said Patterson.

Young swards

Ideally, overseeding should be done into young, clean and open swards, already with some clover established.

Two years in, there aren’t many suitable swards left, so the plan is to reseed some paddocks in the autumn and stitch in clover the following spring.

However, with good weather last autumn, white clover was included in new reseeds sown out on 10 and 20 September, and it seems to have established successfully.

“Maybe it is a bit of a fluke, but I am fairly confident we won’t have to stitch in more white clover – we will see how it goes this year,” he said.

Spray

When it comes to managing weeds, Patterson acknowledged he is “pinning a lot of hope” on ProClova.

He also confirmed that Greenmount has had no issues with bloat in cows, but it is something to be managed more carefully in 2025.

Advice

His advice to farmers thinking of putting clover in across their grazing block, is not to be too ambitious.

“I wouldn’t recommend a four-year transition – it is a big commitment. It has had an impact on silage stocks and we have had to walk cows further to grazing, he said.

There are also plans to establish some red clover in silage swards at Greenmount this spring, confirmed Patterson.