Proporções de nitrato e amônio no cultivo de gergelim sob irrigação com águas salinas.

Abstract

In the semi-arid region, water with high salt concentrations is common associated with the increasing need to expand irrigated agricultural areas, the use of saline waters becomes almost mandatory and, it can cause inhibition of plant growth, ionic toxicity, nutritional deficiencies with consequent reduction of crop production. Thus, it was aimed to evaluate the effects of irrigation with saline waters and fertilization with different proportions of nitrate (N-NO3-) and ammonium (N-NH4+) on the crop of sesame cv. CNPA G3 under greenhouse conditions. The treatments were distributed in randomized blocks, in a 5 x 5 factorial scheme, with three replications, correponding to five levels of electrical conductivity of the irrigation water - ECw (0.6, 1.2, 1.8, 2.4 and 3.0 dS m-1) and five proportions of nitrate (N-NO3-) and ammonium (N-NH4+) (200:0, 150:50, 100:100, 50:150, 0:200 mg kg -1 of soil). Irrigation with saline water higher than 0.6 dS m-1 promotes negative effect on emergence, growth, gas exchanges, fluorescence of chlorophyll a and production components of the sesame cv. CNPA G3, the number of seeds being the variable more impaired. Fertilization with 200:0 mg kg-1 N-NO3-: N-NH4+ provides higher growth in stem diameter, plant height, relative growth rate for plant height and stem diameter, more number of leaves and higher quantum efficiency of photosystem II of sesame cv. CNPA G3. Nitrogen fertilization in the ammoniacal form (0:200 mg kg-1 NO3-: NH4+) promotes increase in the internal CO2 concentration and percentage of cellular damage, besides a deleterious effect on stomatal conductance, water consumption, leaf transpiration and quantum efficiency of photosystem II of sesame. The number of seeds, seed mass, mass of hundred seed, production and water use efficiency are influenced by the nitrate: ammonium ratios, reaching the highest values under fertilization with 150-50 mg kg-1 of N-NO3- and N-NH4+ and irrigation with water of 0.6 dS m-1.