Monitoramento de íons na solução e no extrato de saturação do solo sob aplicação de diferentes concentrações de sais fertilizantes na água de irrigação em bananeira da terra

Abstract

Ferirrigation enables total control of the amount of fertilizer that should be applied to the soil in accordance to the crop requirements. This application of soluble salts to the soil relies on ion monitoring that optimizes the technology. Knowledge of chemical composition of soil solution as well electrical conductivity is important for a sustainable management of fertirrigation. Monitoring nitrate (NO3-) and potassium (K+) is important since both are essential to the development of most crops. Monitoring soil solution ions can be accomplished by soil electrical conductivity that quantifies the amount of salts in the soil. The general objective of this work was to evaluate the concentration of some ions in the soil solution and saturation extract under application of different concentration of fertilizing salts in the irrigation water to banana cv Terra. The experiment was installed following a completely randomized design in a factorial escheme 6x2, with six fertilizing concentrations (1.0; 2.5 e 4.0 g.L-1 of urea and 13.0; 10.0 and 3.0 g L-1 of calcium nitrate) and two trickle irrigation systems (microsprinkler and drip) totalizing twelve treatments. The plot was represented by 20 plants of banana cv. Terra, totalizing 240 plants under single rows of 3.00 m x 2.50 m in na area of 10 ha. The averages of treatments were compared by t test at 5% probability level. Electrical conductivity of saturation extract (CEes) and soil solution (CEw), nitrate and potassium of soil solution were monitored during the first cycle of banana crop. There was a linear elevation of electrical conductivity of saturation extract (CEes) and soil solution (CEw) with the increase on concentration of urea and calcium nitrate of the irrigation water. The use of irrigation water concentrations of 4.0 g.L-1 and 13.0 g.L-1 from injection solutions of urea and calcium nitrate, respectively, yielded CEes and CEw larger than 1.1 dSm-1 during, at least 33% of crop cycle for drip and microsprinkler irrigation systems. The concentration of nitrate in soil solution increased with the concentration of the nitrogen sources in irrigation water. Maximums of nitrate concentrations were observed for concentrations of 4.0 and 13.0 g L-1, respectively of urea and calcium nitrate. Concentrations up to 4.0 g L-1 of urea and up to 10.0 g L-1 of calcium nitrate did not show tendency for nitrate leaching in between 0.20 m and 0.40 m soil depth. It is feasible to estimate potassium concentration in the soil solution from soil water content and bulk electrical conductivity by using equation derived from Vogeler et al., (1996) linear model and potential onde as well potential equation where potassium is estimated as a function of soil solution electrical conductivity. Values of estimated K were close to the observed ones with normalized mean deviation of 10,0%, maximum and minimum deviation of 5,0% and 13,0%, respectively, during the crop cycle.