Renovation of grasslands with grass and white clover – Effects on yield and carbon sequestration

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There is a pressing need to support farmers' decisions on grassland renovation, based on sound scientific evidence regarding its effects on productivity, herbage quality and soil organic carbon stocks. To quantify these effects a long-term experiment with grass/white clover swards was set up at the Lindhof research farm in Northern Germany in 1995. Treatments included control plots of undisturbed grassland as well as 10 grassland renovations starting after 10 (2005) years and repeated on different plots 10 times until 2019, and without and with addition of slurry (equivalent to 240 kg N ha−1 yr−1). Grassland renovation resulted in a significant drop in biomass production in the first year after renovation, and the slightly higher yields in the third year after renovation could not compensate for this drop. Yields from the year of renovation to three years afterwards were generally lower, with average reductions over the 4-year periods of 2600 kg DM ha−1 for the treatments without slurry and 1500 kg DM ha−1 for the slurry treatments. Differences in herbage quality between permanent and renovated grassland were negligible and generally not statistically significant. The soil organic carbon showed a rapid and significant drop in the year of renovation, followed by a gradual increase. Without slurry application, the initial levels of soil organic carbon stocks could not be reached even after a period of 18 years following renovation, and with slurry application, it took about 8–10 years. Deep ploughing to a depth of 30 cm did not increase the SOC stocks compared with the undisturbed permanent grasslands, suggesting that the topsoil has not reached the carbon saturation level. We conclude that maintaining productivity of permanent grassland without renovation measures is a promising way towards yield stability and natural climate solutions.