Caracterização da pastagem, desempenho animal e viabilidade econômica em Coastcross consorciado ou não com Arachis pintoi

Abstract

The research is composed of four articles, with the objective to evaluate the use of grass and legume mixed pasture and, at last, the production system economic analyses. Thus, the experiment was carried out from July 2004 to June 2005 using an experimental design of randomly block in split-plots scheme, with two replications and composed by four treatments, as follow: Coastcross + Arachis without N (CA0); Coastcross + Arachis with 100 kg of N (CA100); Coastcross with 200 kg of N (C200); and Coastcross + Arachis with 200 kg of N (CA200) in four year seasons (split-plots), winter, spring, summer and fall. The experimental area was equivalent to 5.3 ha, subdivided in eight paddocks with 0.66 ha of average size. The animals were managed under continuous grazing and variable stocking rate. Three heifers were used as testers per paddock, with predominant racial standard (Red Angus x Nelore), with eight months old and 162 kg of initial average weight. The first experiment evaluated the forage accumulation rate (FAR) and total forage mass accumulation (TFMA), as well as the chemical composition and dry matter in vitro digestibility (DMIVD) of leaf blade (LB) and sheath + green stem (SGS) fractions of Coastcross and Arachis pintoi whole plant. Treatments with the highest fertilization levels presented FAR superior than the others (P < 0.05), with higher TFMA in summer, followed by spring, fall and winter, with no difference among then. There was no difference (P > 0.05) among treatments for CP, NDF and DMIVD during the year seasons for Coastcross leaf fractions and Arachis pintoi whole plant. The nitrogen fertilization when applied on Coastcross pasture or mixed with forage groundnut provides an increase in the accumulation rate and forage accumulation, with higher productivity on summer when plants received higher fertilizer amounts. The second experiment evaluated animal.s performance (ADG [average daily gain], SR [stocking rate] and LWG/ha [kg of LW/ha]) and xviii behavior (grazing, rumination, standing, lying down and leisure). The grazing behavior was accomplished in two continuous 24 hours periods, on spring and summer, by visual observation. For ADG, there was no difference among fertilized treatments, however there was superiority of CA100 in relation to CA0 (627 and 479 g/day, respectively). The SR was similar among treatments, with exception of CA200 that was higher than CA0 (3.9 and 3.1 AU/ha, respectively). The LWG/ha were higher than 1000 kg/ha/year with the highest gains observed during rainy season (516 kg/ha on spring and summer). The results revealed that animals under grazing prefer feeding in groups and during the day, mainly on the coolest hours. The use of mixed pastures, reinforced by nitrogen fertilization, results in higher animal production. The third experiment evaluated the nitrate dynamics and the soil ammonium profile in same treatments (plots), on spring and summer. Five soil samples were collected in each paddock in a 16 total, on the following depth: 0-0.2; 0.2-0.4; 0.4-0.6; 0.6-0.8; and 0.8-1 m. This operation happened no longer than 15 days after nitrogen application. Mineral- N dynamics on soil profile was studied by regression analyses. The results demonstrated that treatments with legume usually have a higher nitrogen retention capacity, mainly till 0.8 m depth, contrary of treatment without legume, which allows higher leaching on this soil level. A fourth experiment was accomplished using three years of animal production to evaluate the treatments economic viability, through the following indicators analysis: a) cash flow; b) average return rate; c) internal return rate; d) profit index; e) actual net value; and f) pay back. The results of this analysis reflected in a higher income per hectare for treatment without nitrogen fertilizer. This system allows a higher economic return to the producer.