No‐Till Green Manure Termination Influences Soil Organic Carbon Distribution and Dynamics

Core Ideas Soil organic C pools increased under no‐till green manure termination, and this increase persisted over 3 yr following the green manure termination method. Total organic C and particulate organic matter C showed a stronger response to the green manure termination method than permanganate oxidizable C. Tillage effects in labile soil organic C pools may be harder to detect in organic systems with high levels of C inputs. There is continued interest in adopting no‐till practices in organic agriculture. One way to decrease tillage is to implement no‐till termination of green manures. Studies on this novel approach have focused primarily on cash crop performance and weed control. The objective of this study was to examine soil organic C distribution and dynamics as influenced by different methods of green manure termination of a spring‐planted green manure. In this green manure–wheat ( Triticum aestivum L.)–fall rye ( Secale cereal L.)–soybean [ Glycine max (L.) Merr.] rotation three green manure termination methods were compared (no‐till crop roller, spring tillage, and fall tillage). A mixture of hairy vetch ( Vicia villosa Roth)–oat ( Avena sativa L.) was seeded in late May in two trials, the first commencing in 2013 and the second in 2014. Soil organic C was monitored for 3 yr after green manure termination. In Trial 2, total organic C was greater under no‐till green manure termination compared to fall and spring‐till termination (by 2.4 ± 1.2 Mg C ha −1 and 2.3 ± 1.3 Mg C ha −1 , respectively) and the effect remained significant in all 3 yr. In Trial 1, particulate organic matter C was stratified in no‐till and concentrated at the soil surface (0–5cm) and higher overall in no‐till in Trial 2. Overall soil organic C was higher under no‐till green manure termination and the more labile pool of POXc appeared less responsive to termination treatments.