Carbon and nitrogen mineralization differ between incorporated shoots and roots of legume versus non-legume based cover crops

Aims Cover crops (CC) have been widely used to improve soil quality and sustain agricultural productivity. However, the turnover of carbon (C) and nitrogen (N) from different species and parts of CCs incorporated into the soil under Northern European conditions remains unclear. Methods In this study, we examined mineralization of C and N from isolated shoots and roots of two leguminous and two non-leguminous CCs labeled with 15 N tracers in a 100-day incubation experiment at 10 °C. Results After 100 days incubation, the average net N mineralization was 33% from the leguminous CCs and 20% from the non-legumes. Net N mineralization from shoots was 1–15% (% of the N input) higher than that from the corresponding roots, and the net C mineralization accounted for 53–62% and 18–39% of the total C applied with CC shoots and roots, respectively. The C/N ratio of plant residues was a good predictor for net N mineralization, while the lignin concentration was a good predictor for C mineralization from both roots and shoots. Roots of both legume and non-legume CCs caused net immobilization of (unlabeled) soil N, whereas no significant soil N immobilization occurred from shoots with low C/N ratios. Conclusions Our results indicate that different CC characteristics (C/N ratio and lignin) control the turnover of residue N and C, respectively, in the soil. Our results further showed very limited interactions with soil N turnover (no priming effects) when materials with low C/N ratios were applied to soil.