Low N availability is a major limitation in tropical and subtropical pasture systems and one of the main causes for system degradation. Including legumes in forage mixes may enhance soil-N presence and cycling, therefore mitigating the problem. To test this theory, signal grass [Brachiaria decumbens (Stapf) R. D. Webster] litter chemical composition and decomposition after inclusion of calopo {Galopogonium mucunoides Desv.) at 0, 50, or 100% of litter mass was evaluated. Litter samples were collected from both species and incubated by litter bag technique for 0, 4, 8, 16, 32, 64, 128, or 256 d in 2007 and 2008. Biomass decomposition was described by a simple exponential organic matter (OM) decay model (p < 0.0001; Y predicted [the remaining biomass at a given time of decomposition, predicted by the single exponential model] = 91.11-°°°''5itand 94.16-°°°2i7í for year 1 and 2, respectively). Remaining biomass was lower (p < 0.05) in 2007 (28%) than 2008 (54%) following 256 d incubation at least in part because of greater lignin concentrations in 2008 litter. Pure signal grass litter C:N values were 74 to 76% greater (p < 0.05) than pure legume while the inclusion of 50% calopo reduced (p < 0.05) grass ratios by 62 to 64%. Net annual N mineralization increased (p < 0.05) from 27% without legume to 38% with legume inclusion at 50% of the grass litter, a nutrient cycling acceleration of 16% (p < 0.05). This research indicated that the inclusion of calopo will ameliorate N deficiency in soils of a signal grass pasture.

Roots are an important component controlling grassland sustainability. Th ey can act as a C sink of atmospheric CO 2 and supply essential nutrients for plant growth. Pasture management strategies intended to increase forage and animal production can also aff ect root biomass, root composition, and root decomposition. Th is 2-yr study evaluated the eff ects of N fertilization and stocking rate (SR) on root decomposition and root chemical composition of grazed elephantgrass (Pennisetum purpureum Schum. '381') pastures. Treatments consisted of a factorial combination of three SR (2.0, 3.9, and 5.8 animal unit [AU] ha -1 , 1 AU = 450 kg body weight) and three N levels (0, 150, and 300 kg N ha -1 yr -1 ). Greater turnover rates were observed in Year 2 (k = 0.00215 g g -1 d -1 ) than Year 1 (k = 0.00178 g g -1 d -1 ). Increasing SR increased root decomposition linearly (P = 0.05) at 0 kg N ha -1 ; nevertheless, when N was applied at 300 kg N ha -1 , root decomposition decreased (P = 0.003). Nitrogen fertilization reduced root C to N ratio and increased root N and root acid detergent insoluble nitrogen (ADIN) concentrations in Year 1, but no eff ects were observed in Year 2. Root N disappearance followed a negative single exponential model and increased with increasing levels of N fertilization. Pasture management practices such as fertilization and grazing management can alter the root quality and turnover; thus, development of strategies to manage belowground decomposition is a key to long-term grassland sustainability.

Sunn hemp (Crotalaria juncea L.) is an annual legume widely used as cover crop; however, there is potential to use it as forage. The objective of this study was to evaluate forage characteristics of 5 sunn hemp genotypes (HA, nutritive value, N fixation and nematode control), and beef heifer responses (intake and digestibility) to sunn hemp dietary inclusion. Two experiments were conducted at Ona, FL in 2016 and 2017. In Exp. 1, treatments were the factorial arrangement of five sunn hemp genotypes (AU Golden, Crescent Sunn, Ubon, This article is protected by copyright. All rights reserved. Blue Leaf and Red Mini) and two harvesting time (60 d after seeding or flowering) in a randomized complete block design. In Exp. 2, treatments were 100% sun hemp hay, 50% sunn hemp-50% bermudagrass [Cynodon dactylon (L.) Pers] hay, or 100% bermudagrass hay diets distributed in a completely randomized design. In Exp. 1, Crescent Sunn had the greatest HA [15.2 Mg dry matter (DM) ha-1 ], N fixation (81 kg N ha-1) and nematode control (80% reduction). AU Golden had the greatest crude protein (CP) concentration at 60 d after seeding and flowering (155 and 162 g kg-1 , respectively). In Exp. 2, increasing the proportion of sunn hemp in the diet decreased total forage DM intake (1.6, 1.4 and 1.2 as a % bodyweight with 0, 50 and 100% sunn hemp inclusion). Sunn hemp harvested 60 d after seeding is adequate to meet the nutritional requirements of most beef cattle categories but the genotype choice affects HA and nutritive value.

Despite scientific evidence suggesting that warm‐season grasses can respond favorably to K and P fertilization, the increasing costs of fertilizers limit the extent to which these nutrients are used in pastures and hayfields. Two field studies evaluated ‘Jiggs’ bermudagrass [Cynondon dactylon (L.) Pers.] and ‘Floralta’ limpograss (Hemarthria altissima Stapf. and Hubbard) herbage accumulation (HA), nutritive value, and persistence to reduced fertilization strategies during 2012 to 2014. Treatments were allocated in a split‐plot design with N (90 or 180 kg N ha−1, bermudagrass study) or harvest frequency (6 vs. 12 wk, limpograss study) as the main factors and P (0, 8.7, and 17.4 kg P ha−1) and K (0, 33, and 66 kg K ha−1) levels as subplots. Bermudagrass HA increased linearly (up to 377% in Year 3) as K level increased. Similarly, K fertilization increased limpograss HA from 8.4 to 11.6 Mg ha−1 in 2013 and from 5.8 to 15.7 Mg ha−1 in 2014 as K levels increased from 0 to 66 kg K ha−1; however, no effect was observed in 2012. Bermudagrass HA and ground cover decreased from 2012 to 2014 in all K treatments. Conversely, decreases in limpograss HA and ground cover over time were observed only in the control (no K) treatments. Bermudagrass and limpograss crude protein concentrations generally decreased with increased K level. No effects of N or P were observed. Continuous aboveground removal without proper K fertilization is detrimental to bermudagrass and limpograss production and persistence.

Belowground root biomass can respond differently to grazing management affecting grass sward quality and longevity. Linking grazing management with belowground responses is scarce in warm‐climate grassland literature. The objective of this research was to investigate the effect of different stocking rates (SRs) and N fertilization on root chemical composition and decomposition in signalgrass pastures [Urochloa decumbens (Stapf.) R. D. Webster]. The experiment consisted of a factorial arrangement of three SRs (2.0, 3.9, and 5.8 animal units [AU] ha−1; 1 AU = 450 kg live weight) and three N fertilization rates (0, 150, and 300 kg N ha−1 yr−1). Response variables included root remaining biomass and N, root N and lignin concentrations, root C/N ratio, and root lignin/N ratio. Response variables were not affected by SR and N fertilization, except for remaining root biomass. All response variables were affected by incubation time. Root decomposition fitted a single exponential decay model. Remaining biomass was 30% of initial biomass (k = 0.0022 g g−1 d−1) after 512 d. Remaining N was 31% of initial N (k = 0.0007 g g−1 d−1) at the end of the incubation. Remaining root biomass was reduced with increasing N levels for 3.9 AU ha−1, but not for 2.0 and 5.8 AU ha−1. Root decomposition released ∼65 kg N ha−1 during 512 d trough mineralization. Grassland ecosystems have important C stock in their belowground plant biomass, which is relevant for the global C cycle. Therefore, practices that maintain or increase belowground C stocks should be preferred.