Avaliação agronômica, ambiental e zootécnica da associação de sorgo-leguminosa para alimentação de vacas leiteiras

Abstract

This study aimed to evaluate the impact of intercropped production, sorghum with legumes, on the potential for greenhouse effect mitigation, productivity and forage quality, as well, to verify the organic matter losses, aerobic stability, composition and nutritional value of mixed silage, beyond the behavior, production and milk composition of lactating cows fed with these silages. Two experiments were carried out. Experiment I - It consisted of two grain sorghum (Sorghum bicolor L. Moench) evaluation, being the dwarf sorghum (cv. Surgo) and the giant sorghum (cv. Sweet Virginia BMR), in monoculture or intercropped with legumes. The dwarf sorghum was intercropped with legumes as follows: soybean (Glycine max L. var Mitzuko NT); pea (Pisum sativum L. var astronaute.); vetch (Vicia villosa L. var Savane.); Alexandria s clover (Trifolium alexandrinum L. var Tabor.) and common bean (Phaseolus vulgarisL. var Merveille de Venise.), while the giant sorghum was produced in association with two varieties of common bean (Phaseolus vulgarisL. var Neckargold and Alaric) and a variety of Spanish bean (Phaseolus coccineus L. var. Painted Lady). The intercropping dwarf sorghum+soybean and giant sorghum+Neckargold bean were also evaluated considering their form of crop establishment, with four replications each. Data were analyzed using a completely randomized design. It was observed that the intercropped system did not result significant differences in the forage productivity, except among the dwarf sorghum with soybean associations, in standard plant density (16.65 t DM/ha) and low plant density (15.98 t DM/ha), compared to the giant sorghum intercropped with Neckargold beans, for high plant density (7.31 t DM/ha). The association between dwarf sorghum-soybean in pattern density, provided greater carbon sequestration potential (C), with a mean value of 7.35 t C/ha. The carbon sequestration behaved quadratically to the inclusion of legumes, with an increase of 1.56 t C/ha with the concentration of 13% in the forage. It was observed an increase in protein concentration (CP) and reduction of the C/N ratio in the intercropped forages. There was an increase in lignin levels with the association between sorghum-legume. The inclusion of legumes and/or the form of crop establishment did not improve dry matter digestibility (IVDMD) within the same type of sorghum, however, the highest digestibility were observed in association with the giant sorghum. The sorghum intercropping with legumes improves forage quality, especially protein levels, and contributes to the increase in carbon sequestration. Experiment II - For evaluating the nutritional value of dwarf sorghum-soybean and giant sorghum-Neckargold bean silages were used 12 multiparous Prim Holstein cows (PO), grouped into two lots of six animals, based on days in milk, lactation number and milk production. The experimental period was 21 days of adaptation and two experimental periods of 21 days each. The experimental periods were intercalated with a "wash-out" period of 7 days. The data were evaluated by a cross-over design. In the silages, there were higher organic matter losses, resulting from the fermentation process, in the dwarf sorghum-soybean consortium (12.41%), however, the losses in this silage were reduced during the air exposure period, due to its higher aerobic stability. The dwarf sorghum-soybean silage stood out by higher concentrations of DM, CP, and NDIN associated with low ratio ADIN/N-total and lower values of NDF and ADF, providing greater IVDMD. The cows fed with dwarf sorghum-soybean silage urinated more times. The dry matter intake, for silage as for total diet was higher when the cows fed dwarf sorghum-soybean silage. These cows produced higher daily amounts of milk (28.28 kg/cow/day) than cows fed giant sorghum-bean silage (24.38 kg/cow/day) without changes in fat, protein and N-urea concentration. The silage of dwarf sorghum-soybean provided better feed efficiency, for milk production, and kept the positive daily weight gain. The silages with dwarf sorghum-soybean have better nutritional value and acceptability by the animals, as well as, allows better productive performance and milk quality, that the giant sorghum-bean silage.