Avaliação de estratégias de aplicação de esgoto bruto para fertirrigação de capim elefante

Abstract

The form and dose of application of raw sanitary sewage (RS) in the fertigation of agricultural crops should be adequate so that the process is sustainable, efficient and provides full and healthy plant development. The objective this work was to evaluate the influence of RS application form in level bottom furrows, with closed ends, on environmental quality of physical and biotic environment in a fertigation system with elephant grass. Elephant grass fertigation with RS occurred for three uninterrupted years, and the RS application rate was established as function of the amount of sodium (Na) added to the soil (300 kg ha-1 year-1). In the experimental planning, four treatments were established, in two plots the plants received RS and complement the water demand with water from the public supply network (WS), with and without alternating the position of RS application in the furrows (TFA and TFN, respectively). Two experimental control plots were established, in which the plants received mineral fertilization (N, P and K) conventional (MF), and the grass was irrigated with WS, with and without alternating the position of water application in the furrows (TWA and TWN, respectively). Higher average dry matter yields (29.9 Mg ha-1 year-1) and, consequently, higher average macronutrient extraction by plants submitted to TFA (688, 102 and 508 kg ha-1 year-1 were of N, P and K, respectively), being superior to those obtained in the other treatments. The conventional way of applying RS in the furrows (application only at the beginning of the furrows referring to TFN) provided an increase in the NT and Na content in the soil of the initial region of the furrows and the opposite in the contents of P and K. The alternation in the position of RS application in the furrows provided improvements, observing the agronomic factor and the sustainability of the system, due to the better distribution of nutrients in the area, in addition to not causing the persistence of pathogenic organisms in the soil. The bacterial composition of the soil showed a predominance in the phylum of Proteobacteria in all studied treatments. It was possible to establish simplified criteria for defining the dose of EB as a function of the characteristics of the environment and the amount of Na supplied.