Adubação potássica como atenuante do estresse salino no cultivo de pinheira.

Abstract

The pine tree stands out among the Anonáceas due to the striking flavor and its nutritional value, which justifies the need for expansion of cultivated areas, especially in the Northeast region, where water salinity problems are frequent. One of the alternatives to minimize the deleterious effects of salt stress on plants is the adoption of potassium mineral fertilizer management practices, promoting an increase in crop tolerance to salts. Thus, the aim of this work was to evaluate the growth, water status and physiology of the pine tree when subjected to irrigation with saline water and potassium fertilization. The experiment was carried out under field conditions, in drainage lysimeters; the design was in randomized blocks, arranged in a 2 x 5 factorial scheme, whose treatments resulted from the combination of two levels of electrical conductivity of the irrigation water - CEa (1.3 and 4.0 dS m-1) and five doses of potassium (K1 - 50%, K2 - 75%, K3 - 100%, K4 - 125% and K5 - 150%), with four repetitions. Pine plants were evaluated for growth and physiology. The water salinity of 4.0 dS m-1 reduced the synthesis of chlorophyll a, total and carotenoids in pine plants, 210 days after transplanting. Fertilization with doses of 50 to 150% of the K2O recommendation inhibited chlorophyll b synthesis in pine plants irrigated with 4.0 dS m-1 water. The reduction in the quantum efficiency of photosystem II in pine plants grown under 4.0 dS m-1 salinity is related to photoinhibitory damage in photosystem II. Potassium fertilization did not alleviate the stress caused by water salinity of 4.0 dS m-1 in the growth of pine plants, in the period of 151-245 days after transplanting. The water salinity of 4.0 dS m-1 negatively affects the growth in stem diameter and the number of leaves of the pine tree, at 179 and 210 days after transplanting. Potassium doses of up to 150 mg K2O kg-1 of soil resulted in a higher percentage of cell damage and relative water content in the leaf tissues of the pine tree, 210 days after transplanting. The deficit in water saturation decreases with the increase in K2O doses in plants irrigated with water of 1.3 dS m-1. Plants subjected to water salinity of 1.3 dS m-1 and estimated doses of K2O ranging from 88 to 108% resulted in an increase in stomatal conductance, transpiration, CO2 assimilation rate and instant carboxylation efficiency of pine plants, 210 days after transplanting. The greatest relative growth in pine stem diameter in the period of 179-245 days after transplanting was obtained in plants irrigated with water of 4.0 dS m-1 and fertilization with 99% of the K2O recommendation.