Uso de águas salobras e fração de lixiviação no cultivo da cana-de-açúcar

Abstract

Brazil is the world's largest producer of sugarcane. The Northeast has the potential for expansion of the planted area, however, in this region, the salinization of the soil can compromise the crop that is moderately sensitive to salinity. Thus, the objective was to evaluate the growth, productivity, industrial quality, nutritional status, extraction and export of nutrients and sodium by the cane-plant and cane-ratoon irrigated with brackish water and leaching conditions and the productivity of the 2nd ratoon under the rainfed regime. The study was carried out at the Federal Rural University of Pernambuco, Recife, using drainage lysimeters. The RB92579 variety was evaluated in a completely randomized design: five levels of irrigation water salinity (ECw: 0.5; 2.0; 4.0; 6.0; 8; 0 dS m-1) and conditions without (FL1 = 0) and with leach fraction (FL2 = 0.17), corresponding to depth of 100 and 120% of evapotranspiration. Saline levels were obtained by adding NaCl and CaCl2 to the water of local distribution (0.5 dS m-1). The growth of cane-plant and cane-ratoon was evaluated; the diagnosis leaf (leaf +3) of the cane-plant and ratoon was collected to determine the levels of macronutrients, micronutrients, and sodium. At harvest, the productivity of cane-plant, cane-ratoon, and 2nd ratoon was obtained; industrial quality, extraction, and export of macronutrients, micronutrients, and sodium in cane-plant and cane-ratoon. The salinity of the irrigation water reduced the growth, industrial quality, leaf contents of macronutrients, and micronutrients, except calcium, chloride, and sodium in the cane-plant and cane-ratoon. With the exception of calcium, chloride, and sodium, extraction and export were reduced with salinity in the cane-plant and cane-ratoon. The order of extraction and export in cane-plant and cane-ratoon: FL1 (N > K > Ca > Mg > P > S > Fe > Mn > Cl > Na > Zn > Cu) and FL2 (N > K > Mg > Ca > P > S > Fe > Mn > Cl> Na > Zn > Cu). The production of biomass decreased with the increase of salinity in the cane-plant and ratoon. The salinity of the irrigation water of the cane-plant and ratoon promoted a residual effect on the productivity of the 2nd ratoon. The leaching fraction of 0.17 mitigated the effects of salinity on growth, nutritional content, productivity and promoted greater extraction and export of nutrients.