Produtividade e valor nutritivo de genótipos de alfafa sob pastejo. / Productivity and nutritive value of alfalfa genotypes under grazing.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The need for reduction in animal production costs on farms has become crucial to their survival in the market. In order to generate new alternatives research is needed on the factors that limit the success of pasture-based animal production systems. The adoption of species with high forage potential such as alfalfa (Medicago sativa L.), may be a viable option to improve forage productivity and animal performance, associating high production with high nutritive value. From March 2001 to February 2002 the effect of grazing method and genotype on forage productivity and nutritive value was studied. A mob-grazing experiment was carried out at ESALQ/USP in Piracicaba, SP. The experimental design was a randomized complete block with six field replications in a split-plot arrangement. The grazing method factor (continuous stocking, simulated by defoliation every seven days, and rotational stocking, simulated by defoliation every four weeks during the summer season and every six weeks during the winter season) was allocated at random to main plots which were grazed down to 7 cm at every grazing event. The alfalfa genotypes were allocated to the sub-plots, each of which representing a specific combination among agronomic characteristics regarding dormancy class, origin, and grazing tolerance (ABT-805, Alfagraze, Crioula, CUF-101, and Pioneer 5432). Plots were grazed over 295 days without water deficits, as sprinkler irrigation was provided as needed. ABT-805 was the most productive genotype under continuous (26,6 Mg DM ha -1 ) and rotational (18 Mg DM ha -1 ) stocking. Although, Alfagraze showed the lowest production under rotational stocking (13,3 Mg DM ha -1 ) it was the same as that of ABT-805, under continuous stocking (26,3 Mg DM ha -1 ). Pioneer 5432 showed intermediate productivity, with total accumulation of 24,3 (continuous) and 15,3 Mg DM ha -1 (rotational). The nutritive value of whole plant showed significant variation between grazing methods, although no difference among genotypes was found. Forage produced under continuous stocking had higher concentrations of crude protein (CP; 349 g kg -1 ) and in vitro digestible dry matter (IVDDM; 810 g kg -1 ) compared to rotational socking (238,5 and 757,8 g kg -1 , respectively). Fiber concentrations were the opposite of CP and IVDDM as they were lower for under continuous stocking (240 g kg -1 neutral detergent fiber, NDF; 182 g kg -1 acid detergent fiber, ADF; and 34,9 g kg -1 lignin) than under rotational stocking (325, 255, and 50,6 g kg -1 for the same three fractions, respectively). Both the stem fraction and the whole plant samples had better chemical composition and digestibility under continuous than under rotational stocking. The leaf fraction was more variable in terms of nutritive value (CP, IVDDM, ADF, and lignin concentrations) and was affected by genotype, grazing method, and season. ABT-805 and Alfagraze appear to be the most promising genotypes for grazing systems in central Brazil because of their yield performance and nutritive value. Their success, however, will depend on climatic conditions and choice of grazing management.

ASSUNTO(S)

alfalfa yield-related traits genótipos pastejo. genotype morfologia vegetal alfafa nutritive value agronomic characteristics digestabilidade grazing. bromatologia

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