Recuperação de solo degradado utilizando água residuária tratada em sistema agroflorestal no Semiárido

Abstract

Food security and environmental quality depend primarily on two basic resources, soil and water. The expansion of soil degradation, coupled with climate change, represents a major global challenge for the sustainability of current and future societies. The reuse of wastewater in agriculture has been pointed out as a viable alternative since it is the sector that consumes the most available and good quality water. Thus, the objective of this research was to evaluate the effect of deficient irrigation with effluent treated on soil chemistry and mineralogy, biomass production and efficiency in the use of forage palm water, growth and energy characteristics of wood in an agroforestry system in a degraded area in the Brazilian semi-arid region. For this, a field experiment was carried out in a soil degraded by the removal of the surface layers, under agroforestry system with consortium of two forest species, Sabiá (Mimosa ceasalpinifolea) and Aroeira (Myracrodruon urundeuva Allemão) and the forage palm (Opuntia stricta). The experiment lasted four years, with the first two years irrigated and the last two years with the interruption of irrigation. The treatments were arranged in randomized blocks with 10 replicates in three stages according to the annual palm production cycle. Stage 1 (1st cycle): AB0.5 - water supply 0.5 L/plant/week; ET0.5 - treated effluent 0.5 L/plant/week; ET1 - treated effluent 1 L/plant/week. Stage 2 (2nd cycle) all treatments were leveled at a volume of 0.5 L/plant/week, and in stage 3 (3rd and 4th cycles) the treatments were interrupted. Soil samples were collected in the initial condition (before the beginning of the experiment), at the end of two years of irrigation and, at the end of two years of interruption of irrigation treatments, in which chemical, geochemical and mineralogical analyses were performed. The forage palm was collected annually and productivity calculations were performed. In the tree species, growth measurements were performed and at the end of the experiment, the cut was performed for productivity calculations and energy analyses of the wood. Soil fertility improved mainly in the treatment of higher volume of treated effluent. Two years after the suspension of irrigation the residual effect of the irrigated period maintained significantly higher fertility status compared to the initial condition. At the end of the experiment, an incipient process of soiling and alteration in the geochemistry of the silt and clay fractions was observed, with evidence of ilita formation in clay with effluent application. The highest yield, in fresh and dry mass of the forage palm, was obtained in ET1. The residual effect of the treated effluent applied in the 1st cycle promoted increases in productivity up to the 4th cycle of cultivation, in addition to greater efficiency in the use of water by the forage palm. As for trees, the salts present in wastewater applied in the first two years, the growth and production of Sabiá wood decreased and increased in Aroeira. The Treated Effluent in the volume of 1 L/plant/week increased the Yield in Condensed Liquid and decreased the Volatile Materials (MV) of the thrush, while in the aroeira increased the Basic Density and MV, with a decrease in gravimetric yield. The application of wastewater improved the fertility of degraded soil, which was reflected in biomass production and can contribute to the sustainability and food security of family agricultural systems in the Brazilian semi-arid.