Aspectos produtivos, qualitativos e frequência de visitantes florais em espécies de Stylosanthes ssp. na zona da mata seca de Pernambuco

Abstract

The use of rangeland is highly important as an alternative to optimize the sustainability of animal production. However, environmental and management factors affect the development of plants and their morphological and nutritional characteristics. The objective of this study was to evaluate Stylosanthes genotypes (S. seabrana, S. scabra, S. mucronata and Stylosanthes spp. cv. Campo Grande), subjected to different harvest frequencies (56, 77 e 98 days), in the dry and rainy periods through the morphological and yield variability, nutritional value, and the biodiversity of floral visitors. The experiment was carried out at the Sugarcane Experimental Station of Carpina-EECAC/UFRPE, in the years 2017 and 2018. The treatments were randomized in blocks in subdivided plots with four replications. Plant height and width, stem diameter, number of leaves per branch, leaf:stem ratio, number, diameter and length of primary and secondary branches, length and width of main and lateral leaflets, and dry matter production, nutritional value, fractionation of carbohydrates and protein, and frequency, constancy and dominance of floral visitors were evaluated. It was observed effect (P<0,05) of genotypes, harvest frequency, and seasons of the year for the variables height, and stem and width diameter. The S. mucronata and S. seabrana presented greater (53 cm) and smaller (39 cm) plant height, respectively. The 98-day harvest frequency provided greater plant growth. The S. scabra presented a greater number of primary branches in the rainy and dry seasons. The leaf:stem ratio showed an interaction effect (P <0.05) to genotype and season of the year. The S. scabra showed higher leaf:stem ratio in the dry season. S. scabra and Stylosanhtes spp. cv. Campo Grande obtained higher production of dry matter at frequencies of 77 and 98 days. Significant positive and negative correlations were observed between the morphological and productive variables. In the rainy season were observed plants with a higher CP content (184 g kg-1 of DM) than the dry period (153 g kg-1 of DM). The nutritional value of the genotypes was influenced by the interaction (P <0.05) of harvest frequencies x season of the year. The lowest IVDMD (579 g kg-1) was observed in plants subjected to harvest frequency of 98 days in the rainy season. The S. mucronata and Stylosanthes spp. cv. Campo Grande presented higher NDF content (520 g kg-1), ADF (375 g kg-1) and lower lignin (40 g kg-1). S. seabrana and S. scabra presented a higher proportion of the A+B1 and B2 carbohydrate fractions and Stylosanthes spp. cv. Campo Grande showed higher proportion of C fraction in the rainy season. S. scabra presented 15% CP in A fraction. Regardless of harvest periods, Stylosanthes spp. cv. Campo Grande presented a higher proportion (63.85% CP) of the B1 + B2 fraction. S. seabrana showed a higher proportion of the B3 fraction in the rainy season and C fraction in both seasons. Among the observed floral visitors in the Stylosanthes flowers were butterflies, dipterans, dragonflies, wasps and solitary bees Xylocopa, especially the species Exomalopsis auropilosa, Apis melífera, Tetragonisca angustula and Trigona spinipes for presenting more frequent visits. Exomalopsis auropilosa stood out for presenting the highest frequency, dominance and constancy of visits in the dry and rainy seasons. Most visits to Stylosanthes flowers were for pollen collection. Correlations of different magnitudes were observed between climatic conditions and the number of visits. Morphological and yield characteristics, and nutritional value of these genotypes are affected by the frequency of harvest and season of the year. Species of the Apidae family often visit flowers of Stylosanthes genotypes in search of their floral resources.