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da Silva H.M.S.,University of North Florida | Dubeux J.C.B.,University of North Florida | Silveira M.L.,University of Florida | de Freitas E.V.,Pernambuco State Agricultural Institute IPA | And 4 more authors.
Agronomy Journal | Year: 2015

Roots are an important component controlling grassland sustainability. they can act as a C sink of atmospheric CO2 and supply essential nutrients for plant growth. Pasture management strategies intended to increase forage and animal production can also affect root biomass, root composition, and root decomposition. Th is 2-yr study evaluated the effects 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 effects 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. © 2015 by the American Society of Agronomy.

Apolinario V.X.O.,Federal Rural University of Pernambuco | Dubeux Jr. J.C.B.,University of North Florida | Mello A.C.L.,Federal Rural University of Pernambuco | Mello A.C.L.,Brazilian National Council for Scientific and Technological Development | And 7 more authors.
Agronomy Journal | Year: 2014

Litter decomposition is an important pathway of nutrient return on grazed pastures and it may be affected by management practices. The objective of this study was to evaluate the effects of stocking rate (2, 3.9, and 5.8 AU ha-1; 1 AU = 450 kg animal live weight) and N fertilization level (0, 150, and 300 kg N ha-1 yr-1) on signalgrass (Brachiaria decumbens Stapf.) litter decomposition. Signalgrass litter was placed in nylon bags and incubated for 0, 4, 8, 16, 32, 64, 128, and 256 d during 2009 and 2010. Litter decomposition rates differed between years and among incubation times. The decomposition rate was less in 2009 than in 2010 (3.46 and 4.20 mg g-1d-1, respectively). Stocking rate had no effect on litter decomposition rate. Decomposition rates were greater for fertilization with 300 vs. 0 kg N ha-1 yr-1 (4.47 vs. 3.29 mg g-1 d-1, respectively), which resulted in less N remaining in fertilized signalgrass litter. Concentrations of N and lignin as well as lignin/N ratio fit linear plateau models, increasing 7, 151, and 25 g kg-1, respectively, during the 256-d incubation period. The effect of year on residual N and C/N ratios highlighted the need for long-term trials that measure the peaks of nutrient release and availability to plants. Data are needed to guide nutrient management decisions in tropical pastures. Pasture N fertilization may shift the balance between litter immobilization/mineralization, altering N dynamics in the litter pool. © 2014 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved.

da Silva H.M.S.,Federal Rural University of Pernambuco | Dubeux Jr. J.C.B.,Federal Rural University of Pernambuco | dos Santos M.V.F.,Federal Rural University of Pernambuco | de Andrade Lira M.,Pernambuco State Agricultural Institute IPA | And 2 more authors.
Crop Science | Year: 2012

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 (Calopogonium 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 -0.00451t and 94.16 -0.00217t 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. © Crop Science Society of America.

Apolinario V.X.O.,Federal Rural University of Pernambuco | Dubeux J.C.B.,University of Florida | Lira M.A.,Brazilian National Council for Scientific and Technological Development | Lira M.A.,Pernambuco State Agricultural Institute IPA | And 8 more authors.
Crop Science | Year: 2016

Deposition and decomposition of arboreal vegetation represent crucial but poorly understood soil nutrient and organic matter cycling components of warm climate silvopastoral systems. Biomass loss and nutrient release from decomposition bags with leaves (Exp. 1) or branches (Exp. 2) of the arboreal legumes gliricidia [Gliricidia sepium (Jacq.) Kunth] and sabiá (Mimosa caesalpiniifolia Benth.) in a signal grass [Brachiaria decumbens (Stapf) R.D. Webster] silvopastoral system were measured in 2011 and 2012. In Exp. 2, branches were divided into 0- to 3-, >3- to 9-, and >9- to 20-cm circumference classes. The incubated nylon bags were collected 0, 4, 8, 16, 32, 64, 128, and 256 d after placement on the soil surface. Gliricidia leaves and branches, in general, had higher N and lower acid detergent lignin (ADL) concentrations and ADL/N ratios than those of sabiá. Gliricidia leaf biomass loss rates were greater (P < 0.001; k = 0.0038 g g−1 d−1) than those of sabiá (k = 0.0012 g g−1 d−1), as were the branch biomass loss rates (gliricidia, k = 0.0018 g g−1 d−1; sabiá, k = 0.0005 g g−1 d−1). Leaf N release from the fixed amounts incorporated as annual litterfall corresponded to 47 and 14 kg N ha−1 from gliricidia and sabiá, respectively. The differences in concentrations and decomposition rates of the various fractions indicate that the two legume species differ in their nutrient recycling capacities. © Crop Science Society of America.

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