Anatomical and nutritional characteristics of Megathyrsus maximus genotypes under a silvopastoral system

Abstract

Our objective was to measure chemical composition and anatomy of 5 Megathyrsus maximus (syn. Panicum maximum) genotypes, when grown in combination with eucalypts in a silvopastoral system. Cultivars Massai, Mombaça, BRS Tamani, Tanzânia and intraspecific hybrid accession PM44 were evaluated in full sun and a silvopastoral system at 5 different distances from eucalyptus tree rows. The experimental design was a randomized block in split plot with 2 replications. Plots corresponded with genotypes and subplots with sampling points within the system. Total forage and leaf biomass as well as nutritive value und tissue proportions were evaluated. Our results showed a decrease in biomass as radiation incidence decreased. Forage biomass was greatest in BRS Tamani and Mombaça and lowest in PM44. There was a significant interaction between sampling points and genotype for nutritive value variables, such as crude protein, in vitro digestibility of organic matter, cellulose, hemicellulose and lignin-S, while tissue proportions were not affected by the interaction between sampling points and genotypes. Genotype had more pronounced effects on chemical composition and anatomical characteristics than did sampling points. The leaves of Mombaça were the longest and had greatest total cross-sectional area, and this genotype showed greater proportions of sclerenchyma and vascular tissues than other cultivars and the lowest proportion of mesophyll. The greatest proportion of parenchyma bundle sheaths was also found in Mombaça leaves. Genotypes PM44 and Tanzânia had the lowest proportions of sclerenchyma, and PM44 and BRS Tamani had the lowest proportions of vascular tissues. On the other hand, PM44 and Tanzânia had the greatest proportions of mesophyll. BRS Tamani was comparable with the most used cultivars, Mombaça and Tanzânia, and had forage quality slightly superior to that of Mombaça. Tropical grasses growing under shade can potentially produce less forage but with better nutritive value, in terms of chemical composition and tissue proportions, than grasses grown under full sun. However, as the degree of shading in silvopastoral systems does not occur uniformly across the whole area, the improved nutritive value would not be uniform and may not be very prominent overall.