Quantifying cover crop-derived above- and belowground carbon inputs including rhizodeposition

Quantification of carbon (C) input from cover crop shoots, roots and rhizodeposition is essential in order to understand the role played by cover crops in mitigating climate change through soil C sequestration. To evaluate the potential of cover crops to enhance C inputs to soil, the main objective of this field study was to assess the above- and belowground net C inputs from three different cover crop species (oilseed radish, winter rye and hairy vetch) grown at two field sites contrasting in soil texture and N availability (sandy-high-N and loamy-moderate-N). Belowground cover crop-derived C in topsoil and subsoil was assessed by multiple-pulse (CO2)-C-14 isotopic labeling during 3 months of cover crop growth and tracing the assimilated C-14. The total above- and belowground cover crop net C input to 110 cm depth ranged from 1100 to 3200 kg C ha(-1) and was higher at the sandy-high-N site than at the loamy-moderate-N site. The total net C input was highest for radish at both sites. Belowground net C input (0-110 cm) contributed 32-64 % of the total net C input, with the relative contribution greatest from rye. The relative C transferred to soil via rhizodeposition ranged from 27 % to 42 % of belowground cover crop-derived C in topsoil (0-20 cm), but was not affected by either species or N availability. The quantity of C transferred to soil via rhizodeposition ranged from 180 to 290 kg C ha(-1) and was highest for rye at the sandy-high-N site. Using C-14 tracing, our results revealed that up to 39 % of belowground cover crop-derived C was found in the subsoil (20-110 cm). Our results demonstrate the substantial and rarely quantified C inputs via rhizodeposition from cover crops to both top- and subsoil.