Work by Rothamsted Research on grassland reseeding shows that reseeding permanent pasture increases the contrition to climate change without increasing forage yields. But this is mitigated if clovers are included in the seed mixture.

The study, which examined the impact of reseeding on carbon and nitrogen levels, found reseeding with a high sugar grass was only beneficial if sown in a clover mixture, as this reduced the economic and environmental cost of fertilisers.

Lead author Dr Alison Carswell says that these findings demonstrate that farmers and their advisers must think carefully before reseeding permanent pastures. “Nitrogen use is markedly reduced, and the soil releases carbon during reseeding years, with no substantial improvement in grass yields compared to the permanent pasture in the following years,”, she comments.

“The process of reseeding is costly, both environmentally and on yields, so farmers need to consider making savings elsewhere when reseeding. Including clover in their reseed mix means they can reduce fertiliser use and benefit from the financial and environmental gains of that.”

When considering climate change, simulating nutrient budgets across several years found that whilst pasture releases more carbon during reseeding, it returns to acting as a carbon store once the new sward is established. The data comes from Rothamsted’s “Farm Lab” at its North Wyke station in Devon. This beef and sheep farm allows all key nutrients in and out of the farm to be recorded, whether via air, soil, water, plants or livestock.

Dr Carswell comments: “There’s been a lot of discussion recently on the environmental impacts of beef and sheep farming, but the issue isn’t straightforward and many of the conclusions reached have combined information from several different systems.

“Our data on nitrogen and carbon flows through just one farm confirm that sheep and cattle are inefficient in their use of these nutrients. However, grassland reseeding to include legumes within the new sward significantly improved the nitrogen use of the whole system, and if the aim of grassland reseeding is to reduce nitrogen inputs and dependence on chemical fertiliser, then reseeding with clover could provide a viable grassland management option.”

The research over six years at North Wyke modelled nutrient budgets and the efficiency of nitrogen use by beef and sheep at different stages of sward establishment. It compared three treatments: permanent pasture, reseeding with a high-sugar grass, and reseeding with a high-sugar grass and white clover mix. All three had 30 beef cattle and 75 ewes with lambs grazing them, and winter feeding came from each animal’s corresponding treatment. The sward with clover, without additional chemical-nitrogen fertiliser, produced the same amount of herbage as the fertilised permanent pasture, greatly reducing the environmental impact of animals grazed upon it.