Carbon and nutrient dynamics in short-rotation coppice of poplar and willow in a converted marginal land, a case study in central France

Bioenergy woody biomass production shortens the life cycle of carbon and secures energy supplies. However, using fast growing trees in these woody crop systems such as in short rotation coppices (SRCs), implies an increasing risk of depleting the soil nutrient stocks by direct biomass removal and low nutrient return. The aim of this study was to quantify the impact of these woody crop systems after 4 years of growth on the soil quality (C and nutrient cycling) by monitoring tree components (i.e. shoot, litterfall, root system) instead of soils; C and nutrient contents in weed strips were also included into these analyses. Our results indicated that shoot biomass was similar in SRC-P and SRC-W 2 years after planting (4 t ha(-1)). However, after 4 years, willow outperformed poplar (21.9 vs. 8.6 t ha(-1), respectively) removing until 30 % of K soil pool. Litterfall increased between first and second rotation coppices (0.85 vs. 4 t ha(-1)) similarly for SRC-P and SRC-W, indicating biomass exportation and return were strongly imbalanced in SRCs crop systems. N pool in weed strips represented a significant contribution to N cycling in these SRC woody crop systems due to the presence of N-2-fixing plants. However, no differences were detected between poplar and willow crops. In low quality agricultural soils, which are the likely host for SRC implementation, we demonstrated that willow has a higher nutrient accumulation rate than poplar, particularly for K, Mg and P. Weed strips constitute an important reservoir of C and nutrients and should be studied further.