Influence of NO3- : NH4+ ratio on growth and nitrate accumulation in lettuce (Lactuca sativa L. var capitata) in an aeroponic system

Abstract

The influence of different ratios of nitrate or ammonium nitrogen in nutrient solutions on growth, dry matter, the total nitrogen and nitrate content in lettuce (Lactuca sativa L.) cultivar 'Vanity' grown in an aeroponicsystem was studied. Plants were grown with four nutrient solutions with NO 3 - to NH 4 + ratios of A, 100:0; B, 0:100; C, 50:50; D, 86.8:13.2. The highest average weight of 743 g/plant was measured during the first season in lettuce fed with 86.8% nitrate and 13.2% ammonium nitrogen. Treatment with 100% ammonium showed a significantly (p < 0.05) lower harvest compared to others which did not show significant differences. The average nitrate content in the outer leaves was 92%, 40% and 13% lower in the B, C, D treatments, respectively, when compared to nitrate-only fed plants (A = 3497 mg kg - 1 ). In comparison to the outer leaves, a 2-3 times lower nitrate content was measured in the inner leaves. The most suitable with high harvests and low nitrate contents is lettuce supplied with 50% nitrate and 50% ammonium nitrogen in the nutrient solution.