Effect of nitrogen forms on physiological and biochemical constituents of lettuce grown in soilless conditions during different seasons

Abstract

The effect of different nitrate to ammonium ratios (NO3 - : NH4 +: 100:0, 75:25, 50:50, 25:75 and 0:100 respectively) on physiological and biochemical constituents of lettuce crop raised in polyhouse and in open field conditions (control) were studied during three seasons. There were three dates of sowing viz; October (main season) and February and July (off-season). In each season, fresh foliage were harvested three times from each replication of respective treatments at 30 days interval starting from the date of sowing. At each harvest, fresh and dry biomass of shoot, plant height and leaf area were determined. Biochemical constituents including total chlorophyll, carotenoids, total soluble sugars, total starch, total soluble proteins, free amino acids and proline content were estimated. Activities of antioxidant enzymes viz; superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were also determined. In each season, plant growth, yield, biochemical constituents and antioxidants activity peaked when supplied with nutrient solution having NO3 - and NH4 + in the ratio of 75:25. Even in the main season, polyhouse raised crop supplied with this solution gave better results than the crop raised in the field as per recommended practices.