Braquiaria under irrigation in rotational grazing system and soil physical quality / IrrigaÃÃo em braquiÃria sob pastejo rotacionado e qualidade fÃsica do solo

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The seasonality of forage production is a phenomenon of great importance because it is related to the indices of yield and profitability of livestock production. From that results the constant search for new forages and alternatives compatible with the several systems of production as well as the application of new technologies as pasture irrigation and fertilization. Another fact which has called the attention of the researchers is the structural modifications of soil, as compaction in pastures under animal trampling, interfering in the sustainability of production systems. Before this, the objective of the conducting of this research was to evaluate the yield of Brachiaria brizantha cv. MG-5 irrigated or non-irrigated, the nutritive value of the forage produced, animal performance and the effect of irrigation on the compaction of the pasture soil submitted to the trampling by cattle of the Nelore breed in rotational grazing. The experiment was conducted in the period of March, 2006 to March, 2007 on the Minas Gerais State University experimental farm, Campus of Passos â MG, at the coordinates of 19Â S and 43Â W, with average altitude of 700 m above sea level and annual average temperature between 18ÂC and 20ÂC, with maximum of 38ÂC e annual average rainfall of 1709.4 mm. Forage samples were collected through cutting and direct weighing of the forage mass. For soil sampling, undeformed samples were utilized in the shearing resistance assays. For analysis of nutritive value of the forage and animal performance; yield of total dry matter (DM); contents of crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF); dry matter intake (DMI, % of LW); animal live weight gain; contents of minerals P, K, Ca, Mg, S, Cu, Fe, Mn and Zn and the values of in vitro dry matter digestibility (IVDMD) were studied. Total DM yield of irrigated B. brizantha cv. MG-5 was superior in the grazing cycles of early grazing (fall), becoming equal in the later cycles (summer) in comparison with that non-irrigated one. The animals consumed smaller amounts of forage in the irrigated system, but they presented similar live weight gains in the two systems. The NDF contents in the DM of irrigated B. brizantha cv. MG-5 in most grazing cycles were lower than those of the non-irrigated one, even so are considered quite high if considering that 65% is a content limit to tropical forages. The ADF contents in the DM of irrigated B. brizantha cv. MG-5 were lower than those of non-irrigated one, resulting into higher values of IVDMD in the former system. The CP contents in the DM of B. brizantha cv. MG-5 were relatively low, however higher than the irrigated system as compared with the non-irrigated one. Irrigation promoted increases in the contents of Ca, Mg, S, Cu, Fe, Mn and Zn in all the grazing cycles or in most of them. The envelopments of shearing resistance of RYLd at the stress of 0.06 atm for the irrigated pasture presented a shearing stress superior to that of the non-irrigated pasture and of the natural wood. At the stress of 0.33 atm, no differences in shearing resistance among the managements were found. Apparent cohesion was responsible for the possible alterations of soil structure. The values estimated for the correction factor situated very close to 1, their being able to indicate a possible soil compaction in periods of prolonged management.

ASSUNTO(S)

composiÃÃo quÃmica da forragem cycles of grazing, apparent cohesion, soil compaction, chemical composition of herbage, dry matter intake, live weight gain. zootecnia compactaÃÃo do solo coesÃo aparente ganho de peso vivo. ciclos de pastejo consumo de matÃria seca

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