Impacto de frações de lixiviação no acúmulo de sais, eficiência do uso da água e perdas de nutrientes em milho sob estresse salino

Abstract

The use of saline water in agriculture is a recurrent practice in regions with water scarcity. In order to mitigate the negative effects that the presence of salts causes in crops, one of the most used methods is the application of the leaching fraction (LF). However, depending on the amount of water used in LF, this method can contribute to economic and environmental losses. Therefore, the aim with this study was to evaluate how the LF impact the salt accumulation, water use efficiency (WUE) and loss of nutrients in maize submitted to salt stress. For this, physiological, growth and yield variables in maize plants (BRS 2020) grown in soil columns were analyzed. In addition, for the study of nutrient losses and salt accumulation in the system, the concentration of chemical elements in the leaves of maize, in the leachate and in the soil were also evaluated. The experiment was installed in the area of the Meteorological Station of the Federal University of Ceará, Pici campus, Fortaleza - CE, in a completely randomized design, composed of 4 salinity levels of irrigation water - ECw (0.5, 2.0, 4.0 and 6.0 dS m-1), 2 methods of determining the leaching fraction and 7 replications. The experimental plots were composed of a soil column grown with maize. The LF were determined by two methods: AS - Application of LF calculated for each level of salinity, according to the formula proposed by Rhoades; BS - Application of 15% LF calculated from the soil water balance of the experimental plots. The following variables were evaluated: plant variables (growth, gas exchange, chlorophyll index, yield, WUE and leaf contents of chemical elements), leachate variables (pH, EC, NO3, K, P, Ca, Mg, Na, Cl-, Na/K e NO3/Cl- ratios) and soil in different layers (pH, EC, N, K, P, Ca, Mg, Na e Cl-). For all growth and yield variables, there was no difference between the methods of determining LF. In the AS treatment, higher stomatal conductance, lower leaf K concentration, higher N, P and K leaching and lower WUE were observed. In BS, there was a higher level of chemical elements in the leaves of maize and a greater accumulation of N in the soil. Regardless of the LF determination methods, the leaf concentrations of N, P and K decreased due to the increase in salinity of the irrigation water. In the soil, K, Na, Mg and Cl- accumulated in depth. Furthermore, with the exception of K, there was an increase in the levels of these ions as more saline water was applied. In this way, it was concluded that the BS method for maize submitted to the conditions of this experiment presented greater WUE, lesser nutrient losses and lesser water consumption and did not differ from the results of AS in relation to plant growth and yield.