Leguminosa forrageira e suplementação energética na ciclagem de nitrogênio e produção da soja em sistemas integrados de produção agropecuária

Abstract

The objective of this work was to evaluate in the crop-livestock integration system whether nitrogen cycling and the production of soybean (Glycine max L.) in the summer is influenced by the use of legume and supplementation in the production of beef cattle in winter. The work was developed at the Universidade Tecnológica Federal do Paraná - Campus Dois Vizinhos. The experimental design used to evaluate the animal component, variables related to pasture and soybean production was randomized blocks, with 3 treatments and 3 replications. To determine intake and digestibility, pasture and manure production (feces and urine) a double Latin square 3 x 3 was used. The treatments were composed of intercropping between forage species and pasture supplementation, being: Control: black oat (Avena strigosa S.) + ryegrass (Lolium multiflorum L.); Legume: black oat + ryegrass + vesicular clover (Trifolium vesiculosum Savi) and Supplementation: black oat + ryegrass + supplementation (1% of body weight). The pasture was implanted in an area with a 5-year history of croppasture succession. In the year prior to the experiment, corn was used in the crop component. The total amount of nitrogen (N) cycled in the crop/livestock integration system (pasture/soybean) in the 2020/2021 crop was evaluated, considering the total N consumption by the animals, obtained through grazing simulation, the daily nitrogen return through feces and urine collections, and at the end of the experiment the animals were slaughtered to determine the amount of N retained. In the summer, evaluations on the crop component were carried out to determine the nitrogen export by the soybean crop, as well as the grain production of the same; and the rate of dry matter decomposition and nutrient release from post-grazing residual biomass and animal manure. Through animal supplementation, it was possible to increase the stocking rates (21 %), and with that a greater return via feces and urine of nitrogen was observed (38.21 kg ha-1). The N return of post-grazing residue, soybean straw, and soybean grain yield did not differ between treatments. However, the exportation of N in grains had differences between the evaluated treatments, being higher for supplementation, followed by legume and control (242.11; 230.87 and 220.77 kg ha-1, respectively). The amount of nitrogen exported in the body of beef cattle did not differ between treatments, with an average of 5.39 g kg LW-1. Considering the total cycling in the system, the total export averaged 239.2 kg ha-1, not being significantly influenced by the treatments evaluated. A greater return of N (average 227,64 kg ha-1) was observed where there was presence of legume and animal supplementation. Supplementation and inclusion of legume are alternatives to increase the amount of nitrogen returned in integrated agricultural production systems.