Estoques de carbono e nitrogênio e disponibilidade de nutrientes em sistemas silvipastoris em região tropical sub-úmida

Abstract

Livestock is an activity of extensive use of large production areas without replacement of soil fertility, and may contribute to the degradation of pastures. Thus, silvopastoral systems, which integrate in the same area, tree species, pastures and animals are being adopted to improve the microbiological, chemical and physical attributes of the soil, aiming to increase agricultural productivity. In this aspect, the carbon stock, the nutrient cycling and microbial activity was evaluated in the soils of Brachiaria decumbens Stapf. in a consortium with Gliricidia (Gliricida sepium Jacq. Steud) and Sabiá (Mimosa caesalpiniifolia Benth) in the Forest Zone Pernambuco area. Soil samples were collected in dry and rainy seasons up to 100 cm depth at 0, 4 and 8 m of legume range for chemical analysis, and up to 20 cm at 0, 2, 4, 6, and 8 m from the legume range, for microbiological analyzes. It was determined the carbon stock and evaluated the carbon and total organic nitrogen contents (CTO and N-total), carbon of the soil microbial biomass (C-SBM), macro element contents and the fractionation of the organic matter of these soils. The microbial activity was based on basal respiration of the soil (BRS), allowing to evaluate the metabolic quotient. For the C-SBM, the Brachiaria monoculture and the consortium with Gliricidia and Sabiá were statistically similar in depth 0-10 cm, already in BRS. The value of basal respiration in the treatment of brachiaria was superior to the other treatments at depth 0 -10 cm, and the biological evaluations, for the metabolic quotient, Brachiaria monoculture treatments consortium with Gliricidia and Sabiá presented similar behavior. For the quantification of CTO, the consortium of Braquiária and Sabiá had values significantly higher in the 0-10 cm layer, both in the dry season and in the rainy season. For the treatment of consortium between Braquiária and Sabiá, only the distance of 4 m showed lower values of total N. The Braquiaria consortium with Sabiá showed higher values in C stocks at all distances of the legume range. In the quantification of Carbon of the organic matter fractions, the Brachiaria + Gliricidia treatment presented higher values in humic and fulvic acid fractions. In the humina fraction, the Braquiária was superior to the consortiums with Gliricídia and Sabiá. It is noticed that during the seven years, from the implantation, the three managements adopted resembled the biological activity of the soil, but, for the values of C and N total, the consortium with the legumes provided the highest values. The consortium with Sabiá demonstrated potential for soil C inventory. Already for C in the organic matter fractions, Brachiaria and Gliricidia were superior to the other treatments.