Aspectos radiculares de espécies arbóreo-arbustivas em Sistema Agroflorestal e seus efeitos no solo

Abstract

It is known that the Brazilian semi-arid region suffers negative consequences due to environmental conditions and the indiscriminate use of land by man. Agroforestry systems - AFS are alternatives for benefiting the environment and the farmer through the interaction between animals, annuals and perennials. Based on the hypothesis that the amount and composition of the fine roots of arboreal species in AFS in the semi-arid region affect the quantity and the quality of the organic matter of the soil (OMS), the objective was to analyze the arboreal roots of an AFS in relation to the contents of Carbon, nitrogen and lignin, as well as their dry mass, as well as to analyze the soil for the chemical attributes of fertility and for the contents of carbon, nitrogen and lignin. The work was conducted in an agrosilvipastoril system at Fazenda Crioula, belonging to Embrapa Caprinos e Ovinos, located in Sobral - CE. The design was completely randomized (CRD), with subdivided plots and five replications. In the main plots were studied five arboreal-shrub components: A – Catingueira (Caesalpinea bracteosa Tul); B- Pau Branco (Auxemma oncocalix); C – Sabiá (Mimosa caesalpiniaefolia); D – Gliricídia (Gliricidia sepium). In the subplots, two sampling places were studied: A - within the crown projection; B - out of the crown projection. The analysis of the variance was performed and the average was compared by the Tukey test at 5% probability. With the exception of Gliricidia sepium, all species resulted in higher dry matter values of the roots within the crown projection. All roots of the studied species presented higher values of carbon (C) and nitrogen (N) when collected, within the projection area. Auxemma oncocalix resulted in higher lignin content and lignin/nitrogen ratio inside the crown. Auxemma oncocalix resulted in higher lignin content and lignin / nitrogen ratio in canopy. The lowest averages for calcium (Ca), magnesium (Mg), cation exchange capacity (CEC), sum of bases (SB), potential acidity (H+Al) and base saturation (V%) in soil occurred associated with Gliricidia sepium, While the largest are associated with Auxemma oncocalix and Poincianera pyramidalis. When analyzing the collection area, the DC treatment resulted in higher averages only for the values of phosphorus (P) and H+Al in the soil. The species Poincianera pyramidalis resulted in higher values for C and species Auxemma Oncocalix and Poincianera pyramidalis resulted in higher N values of the soil within the area of crown projection. The species Auxemma oncocalix resulted in higher lignin content in the soil within the area of crown projection. It is concluded that from the results of the chemical attributes analyzed the hypothesis is accepted that the quantity and 10 the composition of the fine roots of arboreal leguminous species in AFS in the semiarid affect the addition of organic matter of the soil from the quantitative and qualitative view. Because of the lower levels of chemical attributes and lower values of the lignin / nitrogen ratio among the species studied, Gliricidia sepium is the one that contributes less to soil improvement in AFS in the long term. Among the species studied, Poincianera pyramidalis and Auxemma Oncocalix, present higher values of lignin / nitrogen, resulting in long - term improvement associated to an organic soil matter that takes longer to decompose.