Potencialização dos serviços ecossistêmicos em sistema agrossilvipastoril com adubação nitrogenada

Abstract

The agrosilvopastoral systems, when properly managed, provide several ecosystem services. The objective was to evaluate the dendrometry, biomass, chemical composition of different fractions and estimate the biological nitrogen fixation (BNF) of sabiá, under different levels of nitrogen fertilization in an agrosilvopastoral system. The experiment was conducted at the ICLF Technological Reference Unit -URT of the Brazilian Agricultural Research Corporation (Embrapa), Cocais unit, located in the municipality of Pindaré-Mirim/MA. A randomized block design with four treatments and three replications was used. Each block had 1 ha and was divided into 12 plots of 0.25 ha. The treatments were: no nitrogen fertilization (0 N); application of 100 kg of N ha-1 year-1 (100N); application of 200 kg of N ha-1 year-1 (200 N); application of 400 kg of N ha-1 year-1 (400 N). Two test animals were used per paddock, while the adjustment animals were used based on the DM forage offer per kg of animal live weight. For sabiá evaluation, two collects were carried out with an interval of eight months and 72 trees were selected per collect to determine the plant stand per plot, stem length (SL), density, volume, height of Lorey (hL), diameter in the breast height (DBH), base diameter (BD) and total aerial biomass (leaves and branches). For the chemical composition of total biomass (leaves and branches), crude protein (CP), dry matter (DM), mineral matter (MM), organic matter (OM), nitrogen (N), carbon (C) and C:N ratio, in addition to BNF (leaves) were determined. Statistical analyzes were performed using the ProcMixed program from SAS University. The means of each treatment were compared using the Tukey test, at the 5% probability level. The initial plant stand was 180 trees in 2020; BD (7.58 to 9.52 cm); DBH (6.04 to 7.16 cm); SL (15.6% increase); hL (4.83 to 6.54 cm); tree volume (0.45 to 0.89 m3

); biomass in the leaves fraction (23.2 to 206.3 kg ha-1); biomass in the branch fraction with circumference <4.9 cm (675 to 995.8 kg ha-1); biomass of intermediate branches with circumference 5-10cm (696 to 1,163.9 kg) and biomass of branches with circumference >10cm (increase of 45%), respectively. In the chemical composition of the leaves, the concentrations of MM, N and CP were higher in the second evaluation cycle with 10.69 g kg-1, 2.64 g kg-1 and 16.48 g kg-1, respectively. In the branch fraction < 4.9 cm, the contents of DM, MM, OM, N, C:N and CP differed between the evaluation cycles. In the branch fraction >10, there was a significant difference for variables MM, OM, N and C. In the agrosilvopastoral system, the different doses of nitrogen fertilization did not influence the density, biomass and chemical composition of Sabiá. The BNF of sabiá in the agrosilvopastoral system was not influenced until the dosage of 200 kg of N ha-1 year-1