Massa de forragem e valor nutritivo de capim-braquiária [Urochloa decumbens (Stapf) R. D. Webster] sob pastejo em monocultivo, com ou sem adubação, e em sistema silvipastoril

Abstract

Silvopastoral systems provide significant ecological, economic, and social benefits. These systems can mitigate the negative effects of monoculture on soil by diversifying production through the integration of forestry practices, promoting animal welfare through shading, and enhancing nutrient cycling, which can improve soil fertility, particularly when involving tree legumes. Signal grass (Urochloa decumbens Stapf.) is the most widespread forage species in Brazilian pastures. The hypothesis of this study is that the silvopastoral system with the tree legume sabiá (Mimosa caesalpiniifolia Benth.) improves the nutritional value of Signal grass compared to monoculture, especially without fertilization, without significantly impacting herbage mass. The objective of this thesis was to evaluate herabage mass and the nutritional value of signal grass in monoculture, with or without fertilization (50 kg of N, P, and K ha⁻¹ year⁻¹), and in a silvopastoral system with the sabiá legume, during the rainy season (March to August 2023) and dry season (December 2022 to February 2023 and September to November 2023), in the semi-arid region of Pernambuco, Brazil. The grazing method used was continuous stocking with variable stocking rates, utilizing non-castrated male crossbred Nelore cattle with an average initial live weight of 170 kg. The experimental design was randomized block with three repetitions. The silvopastoral system showed a lower dry mass of green signal grass forage (2045 kg ha⁻¹) compared to the fertilized monoculture (2703 kg ha⁻¹), while it did not differ from the unfertilized monoculture (2327 kg ha⁻¹). Herbage mass was greater during the rainy season (2987 kg ha⁻¹). The silvopastoral system had a lower amount of senescent material compared to the unfertilized monoculture. Additionally, it exhibited a higher incidence of invasive plants compared to monocultures. There were no significant effects of treatments and seasons on the levels of dry matter, mineral matter, organic matter, neutral detergent fiber corrected for ash and protein, and hemicellulose of signal grass (296 g kg⁻¹ DM, 84 g kg⁻¹ DM, 916 g kg⁻¹ DM, 725 g kg⁻¹ DM, and 39 g kg⁻¹ DM, respectively). The crude protein content of the grass in the silvopastoral system was higher (51 g kg⁻¹ DM) than that of the unfertilized monoculture (41 g kg⁻¹ DM) and did not differ from that of the fertilized monoculture (44 g kg⁻¹ DM). However, it was not affected by the time of year. The levels of neutral detergent fiber and acid detergent fiber in signal grass were higher during the rainy season, averaging 794 and 402 g kg⁻¹ DM, respectively. The in vitro digestibility of dry matter of the forage was higher in the dry season (499.8 g kg⁻¹ DM). The silvopastoral system with the sabiá legume, while promoting lower signal grass herbage mass compared to fertilized monoculture, offers nutritional and structural advantages, such as increased crude protein content and reduced dead material, which can enhance animal diet and consumption.