Potential Contributions of Legume Cover Crop Root Biomass to Labile Organic Matter Pools.

Cover crops play an important role in both restoring soil fertility as well as sequestering soil carbon (C). While above ground biomass contributions to C, nitrogen (N), and organic matter pools are well understood, root biomass is less studied. This study aims to quantify root contributions of four legume cover crop species at spring termination prior to cash crop planting. We hypothesized that most root-derived organic matter would accumulate in the upper rooting zone. We used a randomized complete block design with four replications. Species treatments included Pisum sativum (Austrian Winter Pea), Vicia villosa (Hairy Vetch), and Trifolium incarnatum (Crimson Clover). A 7 cm diameter soil core sampler was used to extract cores from the top 10 and bottom 20 cm of soil prior to spring termination in 2012. Roots were hand washed using an elutriation system, dried at 68¡C for 2d, weighed, and analyzed for C and N composition. Crimson clover produced the greatest root mass within the top 10cm of soil, significantly greater than both hairy vetch and Austrian winter pea. At 20 cm depth, root mass values by species were statistically indistinguishable. Root contributions in the top 10 cm of soil were four times greater than that of the 20 bottom cm. This study provides evidence that in systems utilizing legume cover crops in rotation, roots can be a significant contributor to labile soil carbon in upper soil horizons.