As featured in Arable Farming Magazine
Green options to boost soil health
by Arable Farming September 2020
Soil health is being examined more closely as growers look to improve yields without increasing use of costly inputs. Could putting grass in the rotation help? Jane Carley investigates.
Introducing grass into arable rotations could help boost soil health and tackle weeds, and a growing number of arable farmers are looking to benefit from growing grass leys.
It is widely recognised that soil organic matter (SOM) is fundamental to the maintenance of soil fertility and function through the provision of nutrients and energy which drive the biological processes that underpin soil structural development, nutrient and water availability, and increasing SOM is one key advantage of growing grass.
How farms are achieving this in an established arable system is being explored by the Grass and Herbal Leys Farm Network, a partnership between farmers, researchers and industry which is being co-ordinated by ADAS principal soil scientist Dr Lizzie Sagoo.
It has been founded to help quantify changes in SOM and soil health during and after the introduction of temporary grass/herbal leys, and evaluate the wider implications of their introduction into arable rotations.
Dr Sagoo has been studying the benefits of grass leys for soil health and weed control as part of an AHDB Beef and Lamb-funded project working with Norwood Farm, Somerset.
She says: “It is possible to increase organic matter by applying bulky organic materials such as compost and by reducing tillage, but altering the rotation to include grass is considered to be one of the most effective methods.”
The root mass of the ley and, where it is grazed, dung return from livestock, build organic matter, while the avoidance of annual tillage also reduces the loss of soil organic matter via oxidation.
“While we know there is a positive impact, it is hard to quantify,” adds Dr Sagoo.
“How much the soil benefits depends on a number of factors, including how poor the initial soil health was.”
To register for the Grass Leys Network, farmers are required to complete a questionnaire which gathers information on their farms, the driving forces behind considering grass, perceived barriers and any questions they may have.
“Soils have been an important driver for those that have put leys in, along with a different approach to tackling black-grass, as grazing and cutting eliminate seed return, Dr Sagoo says.
“While it was acknowledged growing grass can improve soil quality, it’s more difficult than some other options, not least because you need a use for the grass.”
Grazing is the most common use, but farmers need to decide whether to own stock themselves or to work with a livestock farmer.
“We are seeing some ‘B&B’ cattle agreements where the beef producer retains responsibility for the stock, while the arable farmer is paid a daily rate, possibly plus a bonus for liveweight gain. You will need to set up and manage the fencing and grass – paddock rotational grazing with frequent moves onto fresh grass is a popular system,” says Dr Sagoo.
Sheep are an alternative and some arable farms will already have agreements with sheep farmers to graze forage or cover crops.
“If there is a market for grass locally, you could also bale it and sell it on, or grow grass for seed, but these are niche markets. Providing grazing for livestock is more common, although there are obviously infrastructure costs for fencing, water provision, etc.”
Dr Sagoo suggests given the establishment costs, it is not worth putting in a grass ley for a single year.
“The most common duration is three to four years. If you are hoping to break the black-grass cycle this is not achievable in a year. Many farmers are looking to extend their arable rotation and the minimum three-year ley is a good way to do this.”
It is also important to consider how the land will come out of grass to maximise its benefits.
“Cultivations will oxidise the organic matter, so some of the soil quality benefit of the ley may be lost, although we don’t yet know how quickly it will decline. Direct drilling or minimum tillage should help to preserve the soil quality benefit longer, and we believe that three years of grass in a seven- to eight-year rotation will help build organic matter over time.”
Before and after
Norwood Farm, used for the AHDB Beef and Lamb Project, will offer ‘before and after’ data, having gone into grass in autumn 2017. One field was split into half grass and half arable, and will return to all arable in 2021, allowing the yield boost to be studied, along with cost benefit analysis of the trial.
Dr Sagoo says seed companies can offer a wealth of knowledge on the right herbal or diverse mixes to sow as an alternative to pure ryegrass.
“Legumes in grass/clover mixes and more diverse swards offer benefits including drought resistance – the practical advantage of this depends on the year, of course, but diverse swards can also be more productive, enhance biodiversity and boost forage quality.”
She points out it is also worth getting advice on establishment methods – while grass can be sown in rows with a cereal drill, herbal mixes contain small
seeds which can struggle under this method and may be better broadcast.