Agronomy Journal • Volume 111, Issue 3 • 2019 1 G rassland litter decomposition can be an impor- tant source of nutrients in grazing systems (Dubeux et al., 2007). However, many C4 grass pastures in warm climates receive little or no N fertilizer, resulting in a greater litter C/N ratio, which slows decomposition and increases the potential for soil N immobilization by microbes (Dubeux et al., 2006). Nitrogen fertilization of C4 grass pastures can increase litter decomposition rate and extent in part because of a lesser litter C/N ratio, which favors decomposition and N mineral- ization (Liu et al., 2011; Manzoni et al., 2010). In addition to their concentrations, the forms of C and N in litter are crucial in determining litter decomposition rate and extent (Heal et al., 1997; Silva et al., 2012). For example, Dubeux et al. (2006) found the lignin/N ratio to be a good indicator of decomposi- tion in bahiagrass (Paspalum notatum Flügge) across a range of stocking rates and levels of N fertilization. As litter decomposi- tion progresses, available C and N in litter decrease because of the continuous disappearance of their labile forms accompanied by the formation of new, recalcitrant materials by microorgan- isms (Berg and McClaugherty, 2008; Gijsman et al., 1997). For bahiagrass litter, ~50% of N remaining afer 128 d of incuba- tion was associated with the acid detergent fber fraction and was unavailable for decomposition (Dubeux et al., 2006). Species richness can enhance decomposition of litter (Chapman and Koch, 2007; Chapman et al., 2013), with legume–grass mixtures decomposing faster relative to moderately fertilized or unfertilized grass monocultures (Silva et al., 2012; Kohmann et al., 2018). Greater microbial diversity and availability of N have been credited with driving this efect (Anderson and Hetherington, 1999; Silva et al., 2012); however, interactions among components of mixtures are complex, and their impacts can vary among species in the mixture (Berglund et al., 2013). For example, in legume– grass mixtures in Inner Mongolia, decomposition of grass was accelerated by the presence of legumes, but decomposition of the legume component was not afected by grasses (Zhang et al., 2013). Legume Proportion in Grassland Litter Affects Decomposition Dynamics and Nutrient Mineralization Marta M. Kohmann,* Lynn E. Sollenberger, Jose C.B. Dubeux, Jr., Maria L. Silveira, and Leonardo S.B. Moreno Published in Agron. J. 111:1–11 (2019) doi:10.2134/agronj2018.09.0603 Copyright © 2019 by the American Society of Agronomy 5585 Guilford Road, Madison, WI 53711 USA All rights reserved. AbstrAct Te impact of legume inclusion on the decomposition of aboveground plant litter in grasslands is not well understood. Our objective was to quantify litter decomposition and nutrient disappearance from ‘Pensacola’ bahiagrass (Paspalum notatum Flügge) as afected by N fertilizer or proportion of ‘Florigraze’ rhizoma peanut (Arachis glabrata Benth.) in litter. Five litter treatments (unfertilized bahiagrass [BG], bahiagrass receiving 60 kg N ha –1 [BGN], rhizoma peanut and bahiagrass mixtures in 33–67% and 67–33% proportions [RP33 and RP67, respec- tively], and pure rhizoma peanut [RP]) were incubated for 128 d during each of 2 yr. Decomposition followed a logistic curve with a linear decay between initial and fnal lag phases. Litter treatment did not afect decomposition rate, but RP33 litter decomposed to a greater extent than BG (35 and 43% remain- ing biomass, respectively) due to a longer linear decay period for RP33. At the end of incubation, only 25% of the initial rhizoma peanut component litter mass remained for RP33, whereas 35 and 39% remained for RP67 and RP. Bahiagrass decomposition was not afected by the presence of legume. Bahiagrass mono- cultures showed δ 13 C depletion, and all legume-containing treatments showed δ 13 C enrichment during incubation. Afer incubation, there was less N in legume litter treatments despite similar chemical characteristics to BGN, indicating that other factors, such as microbial diversity, afected mixture decom- position. Recalcitrance of C and especially N increased dur- ing decomposition. We conclude that N return from mixed legume–grass litter is superior to that of unfertilized grass and equal or superior to that of moderately N-fertilized grass. M.M. Kohmann, L.E. Sollenberger, Agronomy Dep., Univ. of Florida, Gainesville, FL 32611-0500; J.C.B Dubeux, Jr., North Florida Research and Education Center, Univ. of Florida, 3925 Highway 71, Marianna, FL 32446; M.L. Silveira, Range Cattle Research and Education Center, Univ. of Florida, 3401 Experiment Station, Ona, FL 33865; L.S.B. Moreno, Embrapa, Palmas, TO, 77008-900, Brazil. Received 24 Sept. 2018. Accepted 17 Dec. 2018. *Corresponding author (mkohmann@uf.edu). Abbreviations: ADIN, acid detergent insoluble nitrogen; BG, litter from unfertilized bahiagrass; BGN, litter from bahiagrass fertilized with 60 kg N ha –1 yr –1 ; OM, organic matter; PDB, Pee Dee Belemnite; RP, rhizoma peanut litter; RP33, litter mixture of 33% rhizoma peanut and 67% bahiagrass; RP67, litter mixture of 67% rhizoma peanut and 33% bahiagrass. core Ideas • Grass reduced lag phase and increased legume decomposition in mixtures relative to monocultures. • Factors besides litter chemical composition, such as microbial diver- sity, afected decomposition. • Legume treatments were enriched and grass monoculture depleted in δ 13 C during decomposition. • Availability of C, and to a greater extent N, decreased during decom- position. Agronomy, soIls, And EnvIronmEntAl QuAlIty Published online March 8, 2019