Morfologia, produção e valor nutritivo de Stylosanthes ssp. sob intensidades de corte

Abstract

The harvest management affects the production, regrowth capacity, and morphological characteristics of forage plants. Additionally, the conservation of forage legumes, such as Stylosanthes, through the haymaking process may help to reduce the negative impact of reduced forage quantity and quality in the dry season on animal production. The objective of this study was to evaluate the morphological and productive variability of Stylosanthes species managed at different cutting heights, to estimate genetic parameters, the forage nutritive value, light interception, survival, and the dehydration curve during the haymaking process. The experiment was carried out at the Sugarcane Experimental Station of Carpina-EECAC/UFRPE. Five species of Stylosanthes (S. scabra A, S. scabra B, S. mucronate, S. macrocephala and S. humilis) were evaluated under three cutting intensities (10, 20, and 30 cm) in the dry and rainy season of the years of 2017 and 2018. The treatments were randomized in blocks with a split-plot arrangement (species were allocated to the main plots and the cutting intensities to subplots), with four replications. The harvest interval adopted was 77 days. The following characteristics were evaluated: plant height and width, diameter of the main stem, number of leaves per branch, number of basal branches, leaf:stem ratio, number of primary branches, diameter and length of the primary branches, and leaflets length and width. The S. macrocephala and S. mucronata species of showed taller plants in all evaluated cutting intensities, with averages of 63; 55 and 48; 48 cm, in the rainy and dry period, respectively. The S. macrocephala and S. mucronata showed the greatest plant width. The S. scabra (5.2) and S. humilis (5.8) showed the largest number of basal branches the rainy season. The S. scabra A, S. macrocephala, S. mucronata, and S. humilis showed the greater number of primary branches in the rainy season (42, 29, 22, 37, respectively). Lesser number of primary and secondary branches, number of leaves per branch, and length of primary and secondary branches were observed in the dry period. The mortality (%) varied among species and year period. The S. humilis forage production was 3.7 and 1.1 Mg ha¹ in the rainy and dry periods, respectively. The average forage production for S. scabra A, S. scabra B, S. macrocephala and S. mucronata was 2.5, 2.8, 2.4, and 2 Mg ha¹, respectively. High heritability was observed for the length of the tertiary branches (73.6) and width of the central leaflet (99.4). The coefficient of genetic variation (CVg) was greater for the number of basal branches (51.7), number of leaves per plant (53.5), width of the central leaflet (29.8), width of the right lateral leaflet (26.1), and dry mass (25.8). The relationship between the coefficient of genetic and environmental variation (VCg / VCe) was greater than 1. The leaf:stem ratio was 0.9 to 1.8 for S. humilis and S. scabra B, respectively. The mortality in the rainy season was 23, 30, 26, 5, and 4% for S. scabra A, S. scabra B, S. macrocephala, S. mucronata and S. humilis, and 30, 32, 43, 17, and 33 % for the dry period, respectively. The S. scabra A and B had an average CP concentration of ~176g.kg¹, lesser NDF (~456 g.kg¹) and ADF (~279 g.kg¹)) and greater IVDMD (696 and 669 g.kg-1, respectively) compared to other species, being considered promising for cultivation. The dehydration process resulted in little variation in the CP concentrations of the studied species, but the NDF and ADF concentrations were increased. The Stylosanthes S. scabra A, S. scabra B, S mucronata, and S. humilis showed lower NDF and ADF concentrations in the hay. The 48h field dehydration period was enough for Stylosanthes species archive the moisture content of less than or equal to 200 g.kg-1, indicating the possibility of hay production in a short period of time. The hay of Stylosanthes species showed good characteristics of chemical-bromatological composition. The variability observed between the accesses of Stylosanthes allows advances in the selection of more adapted materials, in addition to the use of adequate cutting intensity and conservation of the material in the form of hay.