Short-term cover crop carbon inputs to soil as affected by long-term cropping system management and soil fertility

Cover crops (CC) increase soil fertility via recycling of nutrients such as nitrogen (N) and buildup of soil organic matter, whereby CC contributes to climate change mitigation. The carbon (C) input to soil occurs via the input of plant material (shoot and root) and via phyllo- and rhizodeposition. However, the quantity of phyllo- and rhizodeposition from CC is largely unexamined, although this component potentially has a large contribution to microbial stabilization of C. Isotopic labeling with 13C to trace C flows and 15N to determine N2-fixation was conducted to test the short-term effect of the inclusion of winter vetch as a legume species to a CC mixture. The CC mixtures were established in a long-term experiment (1997–2019) with varying use of manure and CC cropping to test the effect of soil fertility on the behavior of the newly established CC mixtures. A significant reduction in the relative net phyllo- and rhizodeposition was observed with higher soil fertility. Interestingly, the quantity of net phyllo- and rhizodeposition was also reduced with higher soil fertility due to the lower relative phyllo- and rhizodeposition, despite a significantly higher CC biomass. Importantly, adjusting for unrecovered root fragments more than halved the calculated phyllo- and rhizodeposition, indicating that many published estimates are substantially overestimated. The use of CC during autumn provides an important window for C storage with both the input of plant biomass and belowground C investment being drivers of C storage