Similar root and stubble biomass carbon in grass–clover leys irrespective of yield, species composition, sward age, and fertilization

Abstract

Background: Crop- and site-specific quantification of non-harvestable aboveground residues and root biomass is essential for predicting management-induced changes in soil C storage. Aims: The aim of this study was to quantify stubble and root biomass C from productive grass–clover leys used for cutting as affected by fertilization and sward age. Methods: Based on an organic long-term dairy crop rotations experiment with 4 years of grass–clover in a six-course rotation, we examined the effects of fertilization (unfertilized and 300 kg total-N ha−1 in cattle slurry) and sward age (1–4-year-old) on herbage yield and composition, stubble biomass, and composition and root biomass of grass–clover ley. Results: Ley duration and fertilization altered plant community composition and aboveground productivity but did not affect stubble and root biomass C. Conclusions: The results question the use of yield-dependent allometric functions for grass–clover ley used in simulation models and life cycle assessments for C accounting in agricultural systems. For predictions of soil C changes, we recommend the use of a fixed stubble-derived C input from grass–clover ley regardless of sward age and fertilization-induced differences in species composition, and herbage yield. Likewise, a fixed root-derived C input for 1-year-old grass–clover, irrespective of fertilization, may be implemented. However, the contribution of continuous rhizodeposition and fine root turnover to root-derived C input need to be accounted for.