Presumed yield benefit of grassland renewal is offset by loss of soil quality

An important motivation for farmers to renew grassland swards (by ploughing and reseeding) is to introduce the most recent grass cultivars that give high yields and high forage quality. However, grassland renewal may affect soil quality negatively due to ploughing. The aims of this study were (1) to compare grass productivity and soil chemical quality of young and old grasslands, and (2) to investigate the relation between soil chemical quality and grass productivity. On clay soil in the north of the Netherlands we measured grass productivity and soil parameters of ‘young’ (5-15 years without grassland renewal) and ‘old’ (>15 years without grassland renewal) grasslands, located as pairs at ten different dairy farms. We selected grasslands with at least 70% desirable grasses (i.e. Lolium perenne and Phleum pratense). We found a lower herbage nitrogen (N) yield in young grassland and no significant difference compared with old grassland in terms of herbage dry matter yield and fertilizer N response. The soil of young grassland contained less soil organic matter (SOM), carbon (C-total) and nitrogen (N-total) compared to the old grassland soil. Grass productivity was positively correlated with SOM, N-total and C-total. The current management practice of renewing grassland after 10 years without considering the botanical composition is counter-productive.