Distribuição de organismos da fauna epigeica, ciclagem de nutrientes e carbono do solo em agroecossistema de mangueira no semiárido

Abstract

The use of plant mixtures in inter-rows of fruit trees associated with non soil turnover can contribute to the diversity of epigeic fauna, nutrient cycling, and soil carbon sequestration in irrigated environments under semi-arid conditions. The aim of this study was to evaluate the diversity of soil epigeic fauna, the rate of decomposition of biomass and release of nutrients from different plant mixtures, and the carbon stock as indicative of the quality and evolution of different patterns of mango crop agroecosystems (Mangifera indica L.), an experiment was carried out in a randomized complete block design, with four replications, in split plots. The plots were two soil management systems, no-tillage (NT) and tillage (T) and three plant mixtures, PM1 - 75% legumes + 25% grasses and oilseeds, PM2 - 25% legumes + 75% grasses and oilseeds, and SV - spontaneous vegetation. The study of the biomass decomposition and nutrient release were conducted using the litter bag method and the epigeic fauna in Provid type traps, adding to the experimental design, in both of the studies, time factor of collect (0, 8, 15, 30, 45, 60, 90, 120, 150, 180, 210, 240, 270 and 315 days) as sub-subplot. Additionally, as a reference for the study of the soil epigeic fauna was used an area under vegetation of Caatinga. In the study of C stock, local sampling factor (in and inter-rows of mango cultivation) was added to the experimental design as subplots, and two reference areas, a preserved Caatinga area, used under the same type of soil, and soil condition prior to the installation of the study. The plant mixture with a higher proportion of legumes (PM1) had the highest rates of decomposition and release of P and K over time, followed by PM2 (25% legumes + 75% grasses and oilseeds) and spontaneous vegetation (SV). Nonetheless, PM1 presented greater accumulation of dry matter compared to SV, its use in agroecosystems in the semi-arid region allows a greater cycling of nutrients over time. The soil tillage system had a negative effect on the diversity of the epigeic fauna, providing the lowest values of abundance, richness, and Shannon indices and Pielou equability. The plant mixture of PM1 and PM2 provided greater richness to the community of the epigeic fauna and higher diversity indexes of Shannon compared to SV, indicating the potential use of these plant mixtures for the increase of soil biodiversity in agroecosystems of fruit trees in semi-arid conditions. There was an increase in the C stock in most of the soil layers, both for the row and inter-rows of the mango crop when compared to the values found at the beginning of the experiment. However, none of the evaluated systems presented higher C stock than the area under Caatinga. The use of the PM1 plant mixture in the inter-row increases the C stock in the mango cultivated in the row. Regardless of the soil preparation system, the agroecosystem design using PM1 is a promising system to increase the total soil stock and fractions of carbon and to increase soil carbon management index in the 0-40 layer cm. Thus, the no-tillage system, associated with the use of plant mixtures in the mango inter-row, is recommended as a sustainable soil management system.