Signalgrass Pasture Research Articles

Strategic Ensilage of Signal Grass Pastures in Two Seasons in a Tropical Region

In tropical regions, grass silage can be produced from the pasture in the rainy season to feed animals during the dry season. We evaluated the chemical composition and fermentation characteristics of ensiled signal grass (Urochloa decumbens Stapf. Basilisk) fertilized with nitrogen (N) or intercropped with calopo (Calopogonium mucunoides Desv.) with and without microbial inoculant. We used a 4 × 2 factorial scheme in a randomized block design, with two blocks and two treatments per block, considering p > 0.05. We studied signal grass fertilized with 0 kg ha−1 of N (0 N), 50 kg ha−1 of N (50 N), or 100 kg ha−1 of N (100 N), or intercropped with calopo legume (LEG), with (I) or without (WI) inoculant, in two seasons. During the dry–water transition, lower concentrations of butyric acid were observed in 50 N and LEG silages (2.77 and 2.55 g kg−1 dry matter, DM) (inoculated) compared to control (7.77 g kg−1 DM). During the water–dry transition, higher concentrations of crude protein were observed in 100 N and LEG silages (71.90 and 54.6 g kg−1 DM) than in 0 N (46.3 g kg−1 DM). The signal grass–calopo intercropping is an alternative to nitrogen fertilization, as it provides forage with a higher protein content and silage with satisfactory fermentative characteristics.

Bioprospecting Fluorescent Pseudomonas from the Brazilian Amazon for the Biocontrol of Signal Grass Foliar Blight

Biological control is considered the only viable integrated disease management practice for controlling the widely distributed and destructive foliar blight and sudden death disease caused by the fungus Rhizoctonia solani AG-1 IA on signal grass (Urochloa brizantha) pastures. Since major signal grass varieties are highly susceptible and fungicide sprays are not labeled for grass pasture cropping systems, biological control is sought as an alternative for managing this fungal disease. In this study, 24 fluorescent Pseudomonas isolates obtained from naturally suppressive soils from the Amazon biome were bio-prospected for their role as biocontrol agents against R. solani AG-1 IA. Based on in vitro antagonism, three isolates (Amana, Poti, and Yara) were selected for further in vivo assays. Multilocus phylogenetic analysis indicated that Amana and Yara were grouped into the Pseudomonas putida group while Poti was grouped into the Pseudomonas asplenii group, and could well constitute a new Pseudomonas species. For in vivo biocontrol assays, the biocontrol agents were applied either via seed-treatment or via foliar spray. All three isolates produced siderophores and solubilized phosphate, while Amana and Poti showed protease and chitinase in vitro activity. Foliar application of P. putida Amana from Amazonian suppressive soils resulted in a significant reduction of the foliar blight disease severity on signal grass. We discuss further steps for the development and labeling of Pseudomonas-based biofungicides for managing the foliar blight disease on signal grass pastures in Brazil.

How does the initial sward height and the grazing period influence the spatial variability of vegetation in deferred signal grass pastures?

The objective of this study was to evaluate the spatial variability of structural characteristics of deferred pastures of Brachiaria decumbens cv. Basilisk (signal grass) subjected to associations of sward heights (10, 20, 30, and 40 cm) at the beginning of deferment and grazing periods (1, 28, 56, 85, and 113 days). The experiment was arranged in a split-plot and completely randomized-block design with two replicates. Pastures remained deferred from March to June 2010. From June to the beginning of October 2010, deferred pastures were utilized by steers under continuous grazing and at a fixed initial stocking rate of 3.5 AU ha-1. At the beginning of the deferment, the coefficient of variation (CV) for pasture height was reduced linearly with the pasture height. During the grazing period, in the winter, the CV for pasture height was not influenced by initial pasture height; however, it responded quadratically to the grazing period, with a maximum value of 36.4% at 71 days of the period of utilization. The CV for tiller height was reduced linearly with pasture height at the beginning of deferment but increased linearly along with the grazing period. The initial pasture height did not change the CV of the falling index. However, the latter was quadratically influenced by the grazing period, with a maximum value of 59.5% at 67 days of the utilization period. Signal grass pastures deferred at a lower height have a higher spatial variability of the vegetation. In the grazing period, there are changes in the spatial variability of the vegetation of the deferred signal grass.

Canopy responses of signal grass cv. Basilisk pastures subjected to three fertilization regimes at two stubble heights

The impacts of fertilization regimes and stubble heights in signal grass cv. Basilisk pastures were evaluated during latespring and summer in Brazil. Liming and N, P and K fertilization were applied to generate gradients in soil fertility tomaintain soil base saturations around 35%, 50% and 65%, increase soil P concentration and the proportion of K in soilcation exchange capacity, combined with two stubble heights of 10 and 15 cm. Herbage accumulation was not affectedby fertilization regimes and stubble height reaching 10 t/ha of dry matter during the growing season. Cutting at 10cm maximizes the leaf mass and leaf area index and decreases dead material mass without the need of high soil basesaturation and NPK fertilization rates to sustain plant growth. However, this stubble height required longer regrowthperiods to attain 95% of light interception (LI95%). A stubble height of 15 cm is preferred when short regrowth periods are required. The canopy height at the point of LI95% does not change with fertilization regimes, but the LI95% is reached at different canopy heights in late spring and summer in signal grass pastures. The adoption of a moderate fertilization regime is recommended as a strategy to obtain an equitable forage distribution between late spring and summer.

Signal Grass Deferred Pastures Fertilized with Nitrogen or Intercropped with Calopo

This study aimed to evaluate the accumulation, structural characteristics, and chemical composition of deferred signal-grass pastures that were subjected to four treatments: without nitrogen fertilization, intercropped with calopo (Calopogonium mucunoides), and fertilized with urea N (50 kg ha−1 and 100 kg ha−1) for 2 years. The design was in randomized blocks, with two blocks and two repetitions of each treatment per block. There were effects of the interaction between treatment and year on green dry mass, forage accumulation, density of vegetative tillers, and crude protein content (simulated grazing). The effects of the treatments on the height, falling index, green dry mass/dead dry mass ratio, number of dead, live and total tillers, and crude protein content (direct cutting) were also observed. Signal-grass–calopo-intercropping ensured adequate mass and forage accumulation and crude protein content equivalent to those of fertilized pastures. In addition, the intercropped pasture showed a higher percentage of leaves and a higher crude protein content compared with those for the other treatments (simulated grazing). The green dry mass/dead dry mass ratio was highest in the intercropped pasture and was equivalent to only that of the pasture fertilized with a low dose of nitrogen. Therefore, signal-grass–calopo-intercropping may be recommended for deferment.

Decomposition of senescent leaves of signalgrass (Urochloa decumbens Stapf. R. Webster) and arboreal legumes in silvopastoral systems

The presence of arboreal legumes in silvopastoral systems (SPS) may affect litter production and quality, and the characteristics and distribution of soil organic matter (OM). Senescent leaves from two tree legumes [Gliricidia sepium (Jacq.) Kunth ex. Walp. (Gliricidia) and Mimosa caesalpiniifolia Benth. (Sabia)] in SPS with Urochloa decumbens Stapf. R. Webster (signalgrass), and from signalgrass pasture in monoculture (Signalgrass), were collected when still attached to the plant and incubated on the ground during 0, 4, 8, 16, 32, 64, 128, and 256 days. Response variables included the disappearance of dry matter (DM), OM, C, N, lignin, acid detergent insoluble nitrogen, and C:N and lignin:N ratio. Single negative exponential models were adjusted to estimate the relative decomposition rate (k). The decomposition rate (k) of DM, OM, and C was greater for Gliricidia and Signalgrass (P < 0.05) compared to Sabia, incorporating 801 g kg DMtotal−1, 850 g kg OMtotal−1, and between 840 and 860 g kg Ctotal−1. Gliricidia showed greater N release rate compared to Sabia and Signalgrass, with an estimated disappearance of 23, 4, and 6 mg N g DM–1 for Gliricidia, Sabia, and Signalgrass, respectively. Tree legumes showed lesser k for C:N ratio and greater for lignin concentration (P < 0.05). Gliricidia had greater release of nutrients to the soil, while Sabia had slower decomposition rates, but with the potential to form a more stable OM because of more recalcitrant compounds left behind. The k of Signalgrass was limited by the lesser N concentration and high C:N ratio in the litter, contributing to immobilization of N during litter decomposition.

Atributos físicos do solo em diferentes sistemas de manejo de agroecossistemas no Território do Caparaó

Comprehending impacts of soil management and use on its physical attributes is essential to develop sustainable agricultural systems. This study evaluated the behavior of soil physical properties under different types of use and management in “Caparao Capixaba” territory, state of Espirito Santo. This study was performed in eight different agroecosystems: Molasses grass pasture (PCG); Signalgrass pasture (PBR); Arabic coffee plantation (CA1 and CA2); Horticulture (HOR); Citrus culture (FRU); Eucalyptus forest (EUC) and Native vegetation (VEN). Gravimetric moisture (GM), bulk density (Bd), particle density (Pd), total porosity (Tp) and soil penetration resistance (PR) were evaluated at 0–10 cm, 10–20 cm and 20–40 cm depths. The highest GM was found in HOR and VEN. The highest Bd were found in the CA2, PCG and FRU management system. At a surface depth (0–10 cm), PBR presented the lowest PT value, statistically equal to CA2 and FRU. The highest values of RP were observed in PBR at all evaluated depths (5.28, 8.32 and 10.68 Mpa). CA1 and CA2 were similar in RP, even when in different places. PCG, PBR, FRU e EUC showed RP higher than 4.0 MPa, which is beyond the critical limit for root system growth. The results indicate that different soil management approaches for the existing crops and vegetation in the agroecosystems can cause significant changes in soil physical attributes.

Legume-based silvopastoral systems drive C and N soil stocks in a subhumid tropical environment

Silvopastoral systems include trees or shrubs and grasses and are considered a sustainable method of restoring degraded pastures and increasing carbon and nitrogen stocks in tropical soils. We hypothesize that establishing shrub-tree legumes in a signalgrass pasture has the potential to increase soil C and N stocks. Thus, we investigated a silvopastoral system over four years in a subhumid tropical zone in northeastern Brazil to determine the soil C and N stocks and the organic matter chemical fractions. The experimental design consisted of i-pure signalgrass (Brachiaria decumbens), ii-signalgrass intercropped with gliricidia (Gliricidia sepium) and iii-signalgrass intercropped with sabiá (Mimosa caesalpiniaefolia). Measurements were taken at 0, 4 and 8 m away from the legume rows and at random in the pure signalgrass pasture. Soil samples were obtained in the second and fourth years after silvopastoral system implementation at 0–10, 10–20, 20–40, 40–60 and 60–100 cm soil depths at each distance in triplicate to produce compound samples. These were used to determine the C and N contents and stocks, as well as the soil organic matter chemical fractions. Within two years, the gliricidia and sabiá soil C stocks directly below the legume row at 100 cm depth increased by 45% and 35%, respectively, while the soil N stock tripled at all distances. The soil organic matter increased over the two years, and the humin proportion in the soil organic matter (SOM) increased in the silvopastoral system soils. Overall, after four years of silvopastoral system establishment, this system showed the potential to store N and achieve soil C stock levels that are within the global average range for these systems.

Dung decomposition of cattle grazing from mixed pastures of Signalgrass (Brachiaria decumbens Stapf.) and tree legumes

The mineralization rate of ruminant manure may influence the fertilization management of pastures. This study aimed to evaluate feces decomposition of heifers grazing signalgrass (Brachiaria decumbens Stapf.) fertilized or not with N, or intercropped with legumes in the dry forest region. Two experiments were conducted; the first one was a CRD that evaluated the evolution of CO2 from a mixture of soil and feces (10:1) during 22 days of incubation in a hermetically sealed bucket with a solution of NaOH 0.5 mol L-1. The second one was a RCBD that evaluated the in situ decomposition of feces in nylon bags in time periods 4, 8, 16, 32, 64, 128 and 256 days after incubation above ground. The single negative exponential mathematical model was adequate (P ≤ 0.0001) to quantify the CO2 evolution of the mixture of soil and feces, indicating that 78% of CO2 was released at the beginning of the incubation, especially for the feces collected in the signalgrass pastures intercropped with Gliricidia sepium (Jacq.) Kunth ex Walp. (gliricídia). After the first 5 days, CO2 evolution was more stable. Remaining biomass in the litterbag along decomposition fitted the single negative exponential model (P &lt; 0.001). Greater relative decomposition rate (k) of bovine fecal biomass occurred for the N-fertilized signalgrass treatment (k = 0.0031 g g-1 day-1) and a lesser rate for the treatment intercropped with Mimosa caesalpiniifolia Benth. (sabiá) (k = 0.0018 g g-1 day-1). Nitrogen fertilization in signalgrass pasture favored the decomposition of bovine feces at the end of 256 days of incubation.

Beef cattle performance on signal grass pastures deferred and fertilized with nitrogen

ABSTRACT The effect of four nitrogen levels (0, 40, 80 and 120kg N ha-1), applied before deferment on the beef cattle production and structural variables on Urochloa decumbens (signal grass) were assessed from January to October 2012 and from January to September 2013. A randomized block design with three replicates was adopted, in an arrangement of repeated measures in time (grazing period). An interaction effect between nitrogen level and grazing period was observed on extended-plant height and herbage mass. As the nitrogen levels were increased, extended-plant height, herbage mass, total herbage allowance, and efficiency of conversion of fertilizer into herbage were increased. Throughout the grazing period, pasture height, extended-plant height, percentage of leaves, herbage and morphological components allowance, and percentages of leaves and stems in the herbage apparently selected by the animal decreased. Nitrogen levels had no effect on average daily gain or gain per area in the first year. A fixed deferment period with increasing levels of nitrogen fertilization on signal grass pastures does not influence the average daily gain per animal, reduces the efficiency of the nitrogen fertilizer and negatively changes the structural characteristics of the pasture.

Root Decomposition of Grazed Signalgrass in Response to Stocking and Nitrogen Fertilization Rates

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.

PSXI-40 Morphogenetic characteristics of signal grass pastures in monoculture and intercropped with forage peanut.

PSXI-40 Morphogenetic characteristics of signal grass pastures in monoculture and intercropped with forage peanut.

Soil attributes of a silvopastoral system in Pernambuco Forest Zone

This research evaluated soil properties in a silvopastoral system using double rows of tree legumes. Treatments were signalgrass ( Brachiaria decumbens ) in monoculture or in consortium with sabia ( Mimosa caesalpiniifolia ) or gliricidia ( Gliricidia sepium ). Treatments were arranged in a complete randomized block design, with 4 replications. Response variables included chemical characteristics and physical attributes of the soil. Silvopastoral systems had greater (P<0.001) soil exchangeable Ca (gliricidia = 3.2 and sabia = 3.0 mmolc/dm 3 ) than signalgrass monoculture (2.0 mmolc/dm 3 ). Water infiltration rate was greater within the tree legume double rows (366 mm/h) than in signalgrass (162 mm/h) (P = 0.02). However, soil moisture was greater in signalgrass pastures (15.9%) (P = 0.0020) than in silvopastures (14.9 and 14.8%), where soil moisture levels increased as distance from the tree rows increased. Conversely, the light fraction of soil organic matter was greater within the tree legume double rows than in the grassed area (P = 0.0019). Long-term studies are needed to determine if these benefits accumulate further and the productivity benefits which result. Keywords : Fertility, legumes, soil physics, trees. DOI: 10.17138/TGFT(6)15-25

Herbage accumulation, plant-part composition and nutritive value on grazed signal grass (Brachiaria decumbens) pastures in response to stubble height and rest period based on canopy light interception

Signal grass (Brachiaria decumbens cv. Basilisk, syn. Urochloa decumbens Stapf R.D. Webster) has been widely grown in the Brazilian tropics over the last 40 years, but management recommendations have been largely empirical and not based on canopy targets. This study was designed to characterise and explain the impact of canopy-based grazing strategies on herbage accumulation, plant-part composition, and nutritive value of signal grass. Treatments were factorial combinations of two stubble heights, 5 cm (SH5) and 10 cm (SH10), and two grazing frequencies, grazing initiated when 95% (LI95) and 100% (LI100) of incoming light was intercepted by the canopy. Rest periods were imposed during summer and autumn of both experimental years. Leaf blade accumulation was greater for LI100 than LI95 (9.5 v. 8.8 t/ha) associated with increased stem accumulation (4.6 v. 3.5 t/ha for LI100 v. LI95). The SH10 pastures produced more stem than SH5 pastures (4.4 v. 3.6 t/ha), with no difference in leaf blade accumulation. In general, SH10 pastures had more residual leaf blade mass post-graze, whereas SH5 pastures combined with higher grazing frequency (SH5-LI95) became more prostrate over time, increasing leaf blade proportion in post-graze forage. Over time, stubble height had more influence than grazing frequency on leaf blade proportion at pre-graze, and SH5 pastures had leafier canopies than SH10 pastures. Digestibility was less under LI100, especially when associated with SH5 stubble (SH5-LI100), regardless of season of the year. To provide optimal leaf blade yield and overall forage digestibility, particularly during warm, rainy seasons, defoliation of signal grass should include pre-graze height varying from 18 to 30 cm (95–100% of light interception) and mean stubble height close to 10 cm.

Rhizoctonia solani AG-1 IA infects both rice and signalgrass in the Colombian Llanos

ABSTRACT Foliar blight and death of signalgrass (Urochloa spp.) pastures are caused by the Rhizoctonia solani fungus. This study aimed at determining which pathogens from the Rhizoctonia species complex are associated with leaf and sheath blight in Urochloa and rice, in the Colombian Llanos. Sympatric areas of Urochloa pastures adjacent to rice cropping areas were sampled using a linear transect system. The pathogens were identified using morphological traits, molecular detection based on specific primers and sequencing of the ITS-5.8S rDNA region. R. solani AG-1 IA predominated as the pathogen associated with foliar blight in all samples from U. brizantha cv. 'Toledo' and hybrid Urochloa cv. 'Mulato'. Besides R. solani AG-1 IA (18 % of the samples), Rhizoctonia oryzae-sativae (71 %) and Sclerotium hydrophilum (11 %) were also detected. In the cross-pathogenicity test, the R. solani AG-1 IA fungus was the most aggressive to Urochloa, while R. oryzae-sativae produced very mild infection symptoms. This is the first report of R. oryzae-sativae and S. hydrophilum associated with the complex of rice sheath blight diseases in Colombia.

&lt;b&gt;Cattle production supplemented on signal grass pastures during the rainy season

The effects of four supplement doses (0, 1, 2 and 3 kg animal -1 day -1 ) on pasture characteristics and on cattle production on Brachiaria decumbens cv. Basilisk pastures in continuous stocking with variable stocking rate were assessed. Experimental design comprised completely randomized blocks with two replications. Concentrate supplementation did not influence mass (4141 kg ha -1 of DM) and production rate of forage (97.6 kg ha -1 day -1 of DM), morphological components and nutrition value in hand-plucked forage. Similarly, the number of live (1.607 tillers m - ²) and dead (636 tillers m - ²) tillers was not affected by concentrate supplementation. There were linear increases in animal performance (from 0.70 to 1.13 kg animal -1 day -1 ), stocking rate (1.9 to 3.8 animal unit ha -1 ) and animal production per area (1.8 to 6.2 kg ha -1 body weight) with supplementation doses. Concentrate supplementation does not change the structural characteristics of signal grass pastures managed in continuous stocking at 20 cm high, but increases animal production.

Tree Legumes Provide Marketable Wood and Add Nitrogen in Warm‐Climate Silvopasture Systems

Warm‐climate grasslands can be degraded by overgrazing and reduced soil fertility. However, legume trees integrated into these systems (silvopasture) can provide long‐term marketable wood for sale and add N to the system. In addition, tree legumes can improve livestock diet by providing high crude protein forage. Our research assessed biomass and N accumulation by tree legumes: gliricidia [Gliricidia sepium (Jacq.) Kunthe] and sabia (Mimosa caesalpiniifolia Benth.) grown in conventionally grazed signal grass (Brachiaria decumbens Stapf) pasture. The seedlings were planted in 2008 and growth rates were measured in 2012 and 2013. One year after the seedlings were planted, in July 2009, the pastures were grazed. Aboveground biomass doubled from 25 to 50 Mg ha−1 between February 2012 and August 2013. The thickest branches contributed the most (p ≤ 0.05) biomass: 58% for gliricidia and 54% for sabia. Leaves represented the smallest (p ≤ 0.05) fraction: 7 to 13% for gliricidia and 4 to 14% for sabia. Leaf and branch nutrient concentrations varied little (p &gt; 0.05) between species and sampling periods. Gliricidia leaf N ranged from 33.6 to 38.0 g kg−1, while sabia leaf N ranged from 26.9 to 38.5 g kg−1. Biologically fixed N in leaves ranged from 30 to 121 kg ha−1. Sabia branches had less moisture and greater lignin, density, and gross calorific power than gliricidia. While thicker branches represent most of the aboveground tree biomass, leaves and thin branches have greater N concentration, representing an important return pathway to the soil.

Physical properties of a Red-Yellow Latosol and productivity of a signalgrass pasture fertilized with increasing nitrogen doses

The physical properties and fertility of the soil are important factors in the formation and establishment of pasture. Changes in physical properties affect the movement of water, air, nutrients and roots, which, in turn, affect the productivity and longevity of pastures. The objective of this study was to evaluate the physical properties of the soil and the dry matter yield of a pasture with signalgrass cv. Basilisk (Brachiaria decumbens cv. Basilisk), fertilized with increasing nitrogen doses (N), on a dystrophic Red-Yellow Latosol. The experiment was conducted on the Fazenda Rio Manso of the Universidade Federal dos Vales do Jequitinhonha e Mucuri, in Couto de Magalhães de Minas, State of Minas Gerais, Brazil. To evaluate the annual forage yield, a split plot scheme in a randomized block design with four replications was used, with N doses (0, 50, 100, 150, and 200 kg/ha/year) in the plots and growing seasons (first and second) in the subplots. For soil evaluation, a split plot scheme was used with N doses (0, 25, 50, 75 and 100 kg/ha/cut) in the plots and three sampling times (prior to the experiment, at the end of the first growing season and at the end of the second growing season) in the subplots in a randomized block design with four replications. This analysis was performed separately at two soil depths (0-3 and 10-13 cm). Forage samples were analyzed for the annual dry matter yield (DMY), and soil samples were analyzed for pre-consolidation pressure (σp), initial soil bulk density (Bd), total pore volume (TPV) and void index (Vd). Higher nitrogen doses increased the dry matter yield of signalgrass pasture and the pre-consolidation pressure of the soil. The total pore volume and void index decreased, and the initial soil bulk density increased, though without promoting soil compaction.

Deposition and Decomposition of Signal Grass Pasture Litter under Varying Nitrogen Fertilizer and Stocking Rates

Increasing pressure on land used for animal production demands more efficient production systems. Soil nutrients required for plant growth are usually the limiting factor in pasture productivity in the tropics. Thus, understanding nutrient cycling in grasslands is crucial to maintaining pasture sustainability where litter deposition and decomposition are important components of the nutrient cycle. This research evaluated the effects of stocking rate [SR; 2.0, 3.9, and 5.8 animal units (AU) ha–1; 1 AU = 450 kg cattle live weight] and N fertilization (0, 150, and 300 kg N ha–1 yr–1) on litter mass and chemical composition in signal grass (Brachiaria decumbens Stapf.) pastures during two grazing seasons [2009 and 2010; 1709 and 2103 kg organic matter (OM) ha–1, respectively]. In 2009, the highest SR treatments (3.9 and 5.8 AU ha–1) had less litter mass accumulation (2093 and 2205 kg OM ha–1, respectively) than the lowest SR (2750 kg OM ha–1). Litter deposition rate was similar among SR treatments and between years, and averaged 26 kg OM ha–1 d–1. Litter N concentration increased with increasing N fertilization only in the second year (8.6 vs. 11.7 g kg–1 at 0 and 300 kg N ha–1, respectively). Nitrogen fertilization reduced litter C/N ratio for the range of SR tested, but the reduction was more pronounced for the lowest SR (53.1 vs. 29.1 for 0 and 300 kg N ha–1, respectively). Nitrogen fertilization mitigated the negative effect of increasing SR on litter mass deposition and chemical composition by stimulating plant regrowth.

Signal Grass Litter Decomposition Rate Increases with Inclusion of Calopo

ABSTRACTLow 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 &lt; 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 &lt; 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 &lt; 0.05) than pure legume while the inclusion of 50% calopo reduced (p &lt; 0.05) grass ratios by 62 to 64%. Net annual N mineralization increased (p &lt; 0.05) from 27% without legume to 38% with legume inclusion at 50% of the grass litter, a nutrient cycling acceleration of 16% (p &lt; 0.05). This research indicated that the inclusion of calopo will ameliorate N deficiency in soils of a signal grass pasture.