Produção de sementes de azevém BRS Ponteio submetido a intensidades de pastejo, épocas de diferimento e adubação nitrogenada em integração lavoura-pecuária

Abstract

The objective of this work was to evaluate the production of ryegrass seeds in an integrated crop-livestock system (ICL) with ryegrass-soybean succession. The treatments consisted of two grazing intensities (moderate and high, by controlling the pasture height, respectively above 15cm and below 10cm), two deferment periods (main tiller death and beginning of flowering) and four doses of nitrogen (N) (0, 25, 50 and 75kg.ha-1) after leaving the animals, in randomized blocks with two replications. The experiment was carried out at Embrapa Pecuária Sul-Bagé, between 2016 and 2018. Annual ryegrass pasture was established through natural reseeding, the grazing was carried out by calves and the soybean was sown soon after the annual ryegrass seed harvest. Grazing until flowering resulted in higher animal performance per area (242kg.ha-1 – p=0.015). After intense grazing until the beginning of flowering, there was a linear response for seed yield with the advance of the N dose (75kg.ha-1 of N – 847kg.ha-1 of seeds). Soybean yield was not affected by N applied soon after deferment, intensity, or deferment periods (2,077kg.ha-1 grains average). Therefore, the proposal for more intense management resulted in higher system productivity (greater grazing intensity and grazing period and higher N doses). However, moderate grazing for a longer period, determined greater performance per animal (890g.animal.day-1 – p=0.045), and determined heavier ryegrass seeds (PMS =1.79g – p=0.025), and better establishment of soybean. After moderate grazing, the aerial mass of soybean plants, in V4, was 289kg.ha-1 (p=0.003), while after intense grazing it was 190kg.ha-1. Grazing to main tiller death also resulted in better soybean establishment (296kg.ha-1 – p=0.048) in relation to the longer grazing period (184kg.ha-1), but without affecting grains productivity. Greater intensity of exploitation of this system results in greater productivity, both animal and ryegrass seeds, without affecting the yield of soybeans in succession. In terms of production, it is the best management option, however, the worst establishment of the soybean crop is highlighted after high grazing intensity and deferment at flowering. Moderate grazing intensity favors greater individual weight gain and greater weight of annual ryegrass seeds, as well as system sustainability, evidenced by better soybean establishment. This management determined higher quality analyzed products.