Getting to the roots of grass breeding

The future objectives of the grass breeding programme at the Agri-Food and Biosciences Institute (AFBI) site at Loughgall mainly relate back to what is happening in the roots of the plant, grass breeder Dr Gillian Young told attendees at an AFBI open day last Wednesday.

“We are looking at going forward in an environment where we have to reduce the amount of Nitrogen (N) applied, where we are working in a drier climate and need to get more carbon into the soil,” she said.

She explained scientists are now looking at the length, volume and area of the root structure, ultimately to make future varieties more drought resistant, and contribute to improved soil health whether by increasing biodiversity, or storing more carbon deeper in soils.

Despite that focus on nutrient efficiency, she said that improving metabolisable energy (ME) content will remain a key objective, as will improving sward longevity to reduce the required frequency of reseeding, which ultimately will benefit the environment.

There is also an increased threat of crown rust and leaf spot, both of which reduce palatability of grass; so disease resistance will be an increasingly important trait to be considered.

It takes over 15 years to develop new varieties and bring them to market, although Young maintained that technologies to potentially reduce this timeline are currently “high up the research community agenda”.

Environmental cost

Setting the scene at the event, AFBI Director Professor Elizabeth Magowan highlighted that NI farms produce enough energy, protein, vitamins and minerals to feed millions of people across the UK, but this comes at a cost for the environment.

“We are nearly victims of our own success,” suggested Magowan, pointing to environmental pressures due to nitrates and phosphates leaching into waterways and the impact of ammonia from livestock housing on air quality and biodiversity at designated sites.

During her presentation, she highlighted the amount of grass grown by the top 10% and bottom 10% of dairy and beef/sheep farms participating in the GrassCheck programme. The top 10% of dairy farms grow an average of 14t dry matter per hectare (DM/ha) and the top beef/sheep farms grow 12.6t. The bottom 10% of dairy farms are at 9t, while the bottom 10% of beef/sheep grow only 4.8t DM/ha.

The obvious conclusion is that there is potential to grow significantly more grass on many local farms, which would allow more cattle and sheep to be fed, adding further to the environmental pressure coming from farming.

However, the argument made by Magowan is that by growing more grass, it can free up land to plant trees, hedgerows, etc, to take in carbon and improve overall biodiversity on NI farms.

Variation in growth within the farmgate

As well as variation in average grass growth across the 50 farms participating in the GrassCheck programme, there is also a wide range between the top and bottom-performing paddocks on individual farms, suggested AFBI scientist Dr Taro Tarahashi.

He said in most situations, the best-performing paddocks will grow twice that of the paddock with the lowest growth.

“It is an opportunity being missed. Very few farmers are aware the range exists until they see the results,” he said, adding that many of the reasons for poor growth are within the control of the farmer.

GrassCheck is now in its 25th season, with the core data still based on plots at AFBI and CAFRE that receive high rates of N (270kg/ha). However, on other plots, significantly less N is now applied (135kg and 67.5kg), while there are also grass clover plots receiving none at all.

The model also predicts growth two weeks ahead. According to Tarahashi, there is an error rate of around 20% in the model, much of which is due to inaccurate weather forecasts.

Improving the quality of feed and forage in the diet of ruminants will mean less methane is produced per kg or per litre, explained Dr Omar Carballo, a scientist at AFBI Hillsborough.

Methane is a potent greenhouse gas produced during the rumination process. The more an animal eats, the more methane is released.

“Methane is basically a waste of energy from the animal,” said Carballo. He added that while both variables are closely correlated, there is a significant range in methane output between individual animals that consume the same amount of feed: “We are looking at what factors might affect methane production.”

The quality of feed is a key issue. Higher grass fibre content (due to cutting or grazing of more mature swards) reduces dry matter intake, resulting in less milk production and higher methane emissions per litre. A study, quoted by Carballo, showed that cows fed 11.3ME silage had 9.2% less methane per litre than cows fed 10.5ME silage.

Research has also identified that higher fat content in the grass leaf (influenced by grass breeding) may result in higher energy in grasses and up to 10-15% lower methane emissions.

Perennial ryegrass (PRG) will typically only support three full leaves, and when a fourth leaf starts to develop, one of these full leaves will start to die away, ultimately lowering grass quality, Janet Montgomery from Barenbrug told attendees at the AFBI event.

She said farmers should always aim to cut and graze PRG at between the 2.5 and 3-leaf stage, which will help maximise quality, allow the plant to regenerate and extend the life of the sward. Consistently grazing swards that are below 2.5 will mean the sward is more like to “flip over in a stressful event, such as dry weather”, she added.

Montgomery recommends up to 10-15% of the farm is reseeded each year, which will help keep grass genetics current and provide an opportunity to fix problems with compaction or weed infestation.

In a new reseed, create a firm and fine seedbed, with the seeds planted “as shallow as you can go with it [seeds] still being in the ground,” said Montgomery.

“Something I see a lot is people driving too fast – it leads to variable depth. Grass seed has very low resilience to being in too deep,” she advised.

Once the new grass can withstand a pluck test (leaves break off and the roots stay in the ground), do a “nip-off graze” with as many light stock as possible, to ensure every plant gets one bite.

“It will encourage the root system and increase tillering. You are rapidly increasing the density of your pasture,” said Montgomery.

She also suggested that in poorer swards, their life could be extended by a couple of years by simply stitching in some seed later in the season, following a silage cut or a tight grazing.

Multi-species swards (MSS) that include herbs such as plantain and chicory, can be slow to start in the spring, but will out-perform traditional ryegrass swards from mid-season on, especially in dry conditions, explained AFBI scientist Dr David Patterson.

A recent trial at AFBI Hillsborough with dairy-origin steers, also shows higher daily liveweight gains for those cattle on MSS versus a grass clover mix.

However, there are challenges with MSS, including around how long the herbs will last and also at establishment.

“Farmers have found that you really need to control weeds before you put the seed in the ground,” said Patterson, who suggested the ideal scenario is to prepare the seedbed, then leave it for any weeds or weed grasses to emerge. Weeds are then sprayed off ahead of the MSS being sown.

At sowing, he pointed out that the seeds are small, so it is important to “drive slowly, gently brushing the surface”, followed by one or two passes with a heavy roller.

Spring tends to be better than autumn. Farmers who have tried MSS have had limited success trying to stitch it into an established sward, advised Patterson.

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