Effect of root Morphology and termination approach on legume cover crop root decomposition

Background/Question/Methods

Winter annual cover crops are grown to improve soil physical properties and nutrient availability, and are commonly mechanically terminated before cash crop planting.  Cover crop roots are predicted to be a major contributor to soil organic carbon (C) and their morphology can influence decomposition, but retention after termination has not been investigated.  Our goal is to investigate the extent to which leguminous cover crop roots contribute to soil C and how this may be affected by root morphology and termination method.  Objectives are to i) determine root morphological differences between cover crops Austrian winter pea (Pisum sativum), crimson clover (Trifolium incarnatum), and hairy vetch (Vicia villosa), ii) measure how two termination methods affect decomposition rate, and iii) determine how available nitrogen (N) and root particle size affect decomposition.  To determine root morphology, plants were grown in PVC cylinders for 12 weeks and analyzed with WinRhizo software.  Field decomposition studies were carried out at two NC sites using a split plot design.  Air-dried roots of three species were placed in mesh bags and buried to a 15 cm depth. Bags were collected 2, 4, 6, 8, 12, and 16 weeks after burial and analyzed for C and N.  

Results/Conclusions

Root morphological differences were observed between species with crimson clover having greater total root length, fine root length, and surface area than other species.  Crimson clover roots also decomposed faster than other species at site one, while differences were not observed at the other.  Roots from all species in rolled plots decomposed faster at one site, while at the second differences were only observed at week 16.  Laboratory incubations are currently being utilized to investigate the role of soil N and root diameter on legume cover crop root decomposition.