Benefícios da aplicação de quitosana no feijão-caupi irrigado com água salobra.

Abstract

To ensure agricultural production with safety, especially in the semi-arid region of Northeastern Brazil, where there is a shortage of low-salinity water and issues of soil and water salinization are frequent, the development of technologies enabling the use of brackish water in irrigation becomes necessary. The use of chitosan is considered an alternative to minimize the deleterious effects of salinity on plants. The objective of present study was to assess the benefits of application of chitosan on the growth, physiology, and production components of cowpea irrigated with brackish water. Treatments were arranged in a completely randomized design, in a 2 × 5 factorial scheme, with two levels of electrical conductivity of irrigation water – ECw (0.6 and 4.0 dS m-1) and five concentrations of chitosan (0; 0.25; 0.50; 0.75, and 1.00 g L-1), with four replicates and three plants per plot. The effects of treatments were evaluated on physiology (relative water content, electrolyte leakage, photosynthetic pigments and chlorophyll a fluorescence), growth (length of stem, leaf area, stem diameter, and number of leaflets) and production components (number of pods per plant, average pod length, number of grains per pod, grain yield, and grain index). Irrigation with water of electrical conductivity of 4.0 dS m-1 negatively affected the relative water content, electrolyte leakage, growth, synthesis of photosynthetic pigments, chlorophyll a fluorescence, grain production, and phytomass accumulation of cowpea cultivar BRS Tapaihum. Nevertheless, the foliar application of chitosan between concentrations of 0.46 and 0.71 g L-1 mitigated the deleterious effects of salinity, reducing the electrolyte leakage and increasing the relative water content, number of leaves, leaf area, synthesis of photosynthetic pigments, photochemical efficiency, grain production per plant, grain index, and root-shoot ratio. Considering the percentage of production loss obtained at ECw of 4.0 dS m-1 compared to plants irrigated with water of 0.6 dS m-1, cowpea was classified as sensitive (decrease > 60%) to the salinity of the irrigation water, with reduction of 72.95%.