Root‐Rhizome Mass and Chemical Composition of Bahiagrass and Rhizoma Peanut Monocultures Compared with their Binary Mixtures

Abstract

Root‐rhizome mass and chemical composition are important determinants of nutrient cycling and soil C accumulation in grasslands. Adding legumes to grass monocultures increases forage nutritive value and N cycling in animal excreta and aboveground plant litter, but the effects of mixtures on root‐rhizome mass and composition have not been studied extensively. This experiment compared belowground responses of rhizoma peanut (RP, Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flüggé) monocultures with those of their binary mixtures, 3 yr after establishment. Treatments were two bahiagrass entries (‘Argentine’ and DF9, receiving 90 kg N ha−1 harvest−1) and two RP entries (Ecoturf and Q6B) in monoculture, and the combinations of each entry of bahiagrass with each entry of RP. Root‐rhizome biomass in Argentine bahiagrass did not differ from mixtures, but it was greater than RP monocultures in the second year. Total N and C contents were greater in 2016 (P < 0.05, 139 kg N ha−1 and 5360 kg C ha−1) than in 2015 (61 kg N ha−1 and 3540 kg C ha−1) across treatments. In 2016, C/N ratio in mixture belowground biomass was equivalent to that of N‐fertilized bahiagrass monocultures. Bahiagrass and RP belowground proportion did not differ among the mixtures. There was a significant change (P < 0.05) in the Argentine δ15N from −0.76 to 1.68‰ from 2015 to 2016, respectively. Results indicated that mixing legumes and grasses is a good strategy to improve storage of belowground N in root and rhizome, even compared with bahiagrass fertilized with 90 kg N ha−1 harvest−1.