Desempenho animal e ciclagem de nutrientes em sistemas silvipastoris na Zona da Mata de Pernambuco

Abstract

The objective was to evaluate animal performance and nutrient cycling in signalgrass grown in monoculture or in silvopasture systems with tree legumes. The experiment was conducted at the Experimental Station of Itambé, at the Agronomic Institute of Pernambuco (IPA). The experimental area consisted of nine paddocks with 1.0 ha each. Treatments included: 1) Brachiaria decumbens Stapf + Mimosa caesalpiniifolia Benth; 2) Brachiaria decumbens Stapf + Gliricidia sepium and; 3) B. decumbens in monoculture. The design was in randomized complete blocks with three replications. Crossbred Holstein x Zebu steers were the experimental animals. They were managed under continuous stocking with variable stocking rate. Stocking rate was adjusted using the “Put and Take” technique using herbage allowance as a criterion to adjust. Target herbage allowance was 3 kg green dry matter kg liveweight-1., Biomass and N concentration of forage and litter at different distances of tree legume rows (0, 1.8, 3.7, 5.6 and 7.5 m), and soil analysis at these same distances and at three different depths (0-10, 10-20 and 20-40 cm). Herbage mass was greater for brachiaria in monoculture with a mean of 5,057 kg ha-1 of DM when compared to the consortia with a mean of 3,292 kg ha-1 of DM, however, the proportion of green leaf treatments ranged from 46% to 71%. There was interaction (treatment x evaluation date) for dry green herbage mass (DGHM). Treatments showed changes throughout the evaluations, with the greatest average observed in the fifth evaluation (2722 kg DGHM ha-1). Herbage allowance varied from 1.29 to 3.07 kg DGHM KG-1 BW. The live weight gain per animal did not vary among treatments, only between the evaluations occurring weight loss in the month of December -0.05 kg UA-1 day-1, being the highest gain recorded in July 0,97 kg UA-1 day-1. The gain per area was higher in July with 68 kg PV ha-1 28 days-1. The accumulation rate ranged from 15 kg DM ha-1 day -1 to 56 kg DM ha-1 day -1. Stocking rate peaked in cycles 5 and 7. In the evaluation of productive characteristics in distal points from tree legumes, it was observed that signalgrass was taller with greater distances from the trees (7.5 and 5.6 m). Herbage mass at 7.5 m from the tree row varied from 1335 to 3631 kg DM ha-1. Signalgrass in monoculture presented greater herbage mass and was taller compared with signalgrass in consortium. Nitrogen concentration in signalgrass ranged from 14 to 15,6 g N kg-1. Litter N concentration ranged from 12 to 23 g N kg-1, with the lowest value at 7.5 m distance from the tree and the greatest under the tree. The forage density varied according to the time of year, with higher density observed in July 2015 with 202 kg DM ha-1 cm -1. Animal performance was reduced with the tree growth, especially in the sabiá system, likely due to greater competition of the trees with the grass. The greatest contribution of nitrogen was found near the trees, for both brachiaria and litter.