Qualidade biológica do solo irrigado com águas residuárias

Abstract

The use of deposable resources such as sewage wastewater could provide added economic and environmental benefit. Besides improve soil humidity in agricultural activities, the wastewater addition enhances nutrient apport to the crop, especially in association with leguminous plants. Microorganisms immediately response to the environmental shifts signing soil improvement or degradation. The objective of the work was to evaluate the effect of treated domestic sewage effluent on development of colored cotton BRS Rubi and Crotalaria spectabilis as well the effect on soil biological quality and microbiota. Two experiments were implemented. The first experiment was carried out in field, in Ibimirim - PE, Brazil, in a completely randomized design with four treatments (water supply, UASB (Upflow Anaerobic Sludge Blanket) reactor, decant-digester effluent + anaerobic filter, and effluent from anaerobic filter) and six replications, in a 228-m2 area. Evaluations based on development and productive of colored cotton cultivar BRS RUBI, soil humidity and C-CO2 evolution, nematode community, and ecological index. The treated domestic sewage effluent application increased stem diameter, leaf area, and plant height of the colored cotton, but did not affect crop production, soil humidity and C-CO2 evolution comparing to water supply. The bacterivorous nematodes were the most abundant, and the omnivorous the less one. The plant-parasite index was the most sensitive to disturbers from the effluent application. The second experiment was carried out under greenhouse in a completely randomized design and factorial arrangement 4 (water supply and 50, 75, and 100% domestic sewage wastewater treated in UASB reactor) × 4 (a Rhizobium native stirp from the "Zona da Mata" of Pernambuco (CRO), a recommended stirp for green fertilization and cowpea (BR 3267), a control with nitrogen fertilizer (urea 50 kg ha-1), and an absolute control (without inoculant an nitrogen fertilizer), with four replications. All treated domestic sewage wastewater concentrations as well both Rhizobium stirpes and the nitrogen fertilizer did not significantly affect most of evaluated parameters of soil microbiota and plant growth. The inoculant BR 3267 was less successful in increasing the plant fresh biomass than the nitrogen fertilizer. The C. spectabilis nodulation was efficient despite domestic sewage wastewater concentration, except 100%.