Decomposição de resíduos de leguminosas Arbóreo-Arbustivas e liberação de nutrientes no solo

Abstract

The association of legumes with nitrogen-fixing bacteria is relevant for green manure. In this form of fertilization, the supply of nutrients occurs from the decomposition of legume biomass, which must be studied considering the residues of different species under different edaphoclimatic conditions. In this work, the objective was to evaluate the loss of mass and nutrients over time of shoot residues of two legume species in sandy soil, as well as changes in the soil. An experiment was conducted in the greenhouse of the DCS/UFC (Fortaleza, CE), in completely random design in split plots over time with two factors and four replications, totaling 32 experimental units consisting of pots with a capacity of 15 kg of soil. The treatment factors were leaves and branches of two legumes (Gliricidia sepium e Mimosa caesalpiniaefolia) and four evaluation periods (0, 30, 60 and 90 days). The pots were filled with sandy soil and litterbags containing 20 g of fresh legume residues were deposited on its surface. The loss of dry mass and nutrients in the residues in each evaluation period was evaluated, as well as the chemical attributes of the soil. In 90 days, there was a loss of 62.42% of dry mass of G. sepium and 29.18% of M. caesalpiniaefolia. For both species, the loss of biomass was more accentuated in the first 30 days of evaluation, reaching 53.0% for G. sepium and 19.0% for M. caesalpiniaefolia. The residues of G. sepium showed higher nutrient content at the end of the evaluation, higher decomposition rate and nutrient release, especially for Ca and Mg, which were the elements with the lowest k values and the highest half-life values in relation to M caesalpiniaefolia. The residues of G. sepium and M. caesalpiniaefolia promoted improvements in the chemical attributes of the soil, especially N, P, Ca, Mg, CTC, SB and V%, however, the contribution of N by legumes was more evident at 30 days. Soil pH was influenced by the addition of M. caesalpiniaefolia residues, reaching values below 4.6 at 30 days and above 5.0 at 60 days. The potential soil acidity was influenced by both species, reaching higher values at 30 days and lower values at 60 days after addition of residues compared to potential acidity in the soil before the application of residues on the soil in the experimental units.