Efeito da concentração da solução nutritiva em cultivares de alface em sistema hidropônico tipo NFT, em clima semiárido

Abstract

In regions with arid and semi-arid climates, irrigation is a technology that can guarantee profitable plant production throughout the year, but this practice demands great water demands. This problem is potentialized in the Brazilian Northeast where the intensification of droughts observed in recent years , has reduced the water levels of the reservoirs, in some cases reaching zero quota. The hydroponic system in NFT (laminar flow technique of nutrients) is presented as an alternative production, making efficient use of water, where water losses are reduced to practically zero. The objective of this work was to evaluate the biometric variables, gas exchange and nutritional composition of three lettuce cultivars under hydroponic NFT cultivation in different concentrations of nutrients in the nutrient solution in the semi-arid climate of the municipality of Tauá-CE. The experiment was conducted in an agricultural greenhouse of the Federal Institute of Education, Science and Technology of Ceará, Campus Tauá. The NFT system used in the experiment consists of four benches, each with three PVC pipes with a diameter of 75 mm and 6 m in length, with spacing between holes of 0.25 m and slope of 3%. The experiment was set up in a completely randomized design in subdivided plots (4 x 3), with four electrical conductivities of the nutrient solution (0.9, 1.2, 1.5, 1.8 dS m-1) ) and in the subplots three lettuce cultivars (Elisabeth; Cinderella and Mimosa), totaling 12 treatments. Each subplot accommodated 24 plants. At 45 days after the emergency, an evaluation of the gas exchanges was made, after which the plants were harvested and biometric evaluations were carried out and the plants were submitted to oven drying to evaluate the nutritional status. The collected data were submitted to analysis of variance by the 1% F test and 5% probability. The gaseous changes of the plants were influenced by the electrical conductivity of the nutrient solution, the intermediate values for this factor maximized the gas exchange in the cultivars Elisabeth and Cinderela. Considering the fresh mass of the aerial part, the mimosa cultivar obtained the largest weight of 295.93 g plant-1, differing statistically from the others. In all cultivars, the increase in the electrical conductivity of the nutrient solution linearly increased all the biometric variables of the aerial part of the plants. The maximum value for the SPAD index (21.66) was obtained with the electrical conductivity of the nutrient solution of 1.48 dSm-1. The decreasing order of nutrient deposition in the leaves was: K> N> Ca> P> Mg> S> Fe> Mn> Zn> Cu> B. The elevation of the electrical conductivity of the nutrient solution reduced the water consumption of the plants, ranged from 4.65 to 5.93 liters per plant per cycle.