Dinâmica e distribuição dos nutrientes do efluente do tratamento preliminar de esgoto doméstico no solo quando aplicado em sulcos na fertirrigação do capim-elefante

Abstract

Fertigation as an alternative of final disposal of domestic sewage is a viable solution, due to the low implantation cost, the use of nutrients by the plants and the amount of organic matter that acts in the structuring of the soil. In this work, the dynamics and nutrient distribution of the effluent from the preliminary treatment of domestic sewage (PDS) in the soil, when applied in furrows, was evaluated in the fertigation of elephant grass (Pennisetum purpureum). By hypothesis, PDS applied with sequential inversions in the direction of flow in the grooves, in order to obtain a greater homogeneity in the distribution of the nutrients in the soil and, consequently, greater productivity of the elephantgrass. The experiment consisted of 4 treatments: conventional fertilization (using commercial chemical fertilizers - CF) of the elephant grass without alternating in the direction of water flow from the COPASA supply network, applied in the grooves (TAS), conventional elephant grass fertilization with alternation in the direction of flow of water applied to the furrows (TAC), fertigation of elephant grass without alternation in the direction of flow of EDP applied in the furrows (TFS), Fertigation of elephant grass with alternation in the direction of flow of EDP applied to the furrows (TFC). In order to evaluate soil nutrient distribution, N, P, K, Ca, Mg and Na contents were measured in the soil, at the center, at the sides and along the length of the grooves. The nutrient doses contributed to the soil by the PDS were 296 kg ha-1 of N, 43.6 kg ha-1 of P and 87.8 kg ha-1 of K. The yield of elephantgrass was evaluated according to the amount of dry matter (DM). An analysis of the economics of water and financial resources was also made with the use of PDS in the production of elephantgrass. The productivity presented in the second cut of the elephant grass, obtained after 45 days of the first one, was of 6.5 t ha-1 of DM, in the plot with CF without alternating in the direction of water flow; 5.3 t ha-1 of DM, in the CF plot with alternation in the direction of this flow; 4.9 t ha-1 of DM, in the fertigated plot without alternation in the flow direction of the PDS and 14.2 t ha-1 of DM, in the fertigated portion with alternation in the direction of this flow. The alternation in the direction of application of PDS increased in almost 3 times the grass productivity. The use of EDP in elephant grass cultivation provided a total financial saving of US$ 630.00 ha-1 and 58% of the total water demanded by the crop.