EFFECT OF NITROGEN FERTILIZER ON LETTUCE NUTRITION IN PURPLE SOILS

Effects of nitrogen fertilizer on lettuce plant growth, nutrient metabolism and quality were studied in a pot experiment with three purple soils. Lettuce growth traits, such as plant height, root weight, stem and leaf yield, all of which were decreased obviously by applying high and medium levels nitrogen fertilizer in calcareous purple soil, whereas the best response of lettuce to nitrogen fertilizer appeared in neutral purple soil. The percentage of NO3--N/TN and AAN/TN in lettuce leaf in acid purple soil, the former was the lowest, but the latter was the highest. The apparent recovery rate of nitrogen for lettuce order was neutral purple soilacid purple soil. calcareous purple soil. The coefficeient of variation of N/P, N/K and K/P ratio value in lettuce leaf at three growth stages were minimum and plant biomass were maximum at 133, 67 and 67 mgN/kg in neutral, acid and calcareous purple soils, respectively. The application of nitrogen fertilizer to neutral and calcareous purple soils could increase significantly the NRA of lettuce leaf (r values 0.9275* -0.9956* *) and reduce the CAT as well as Vitamine C content, the NO3-/FN ratio values in lettuce stem were inhanced about 2~5 times, relative to that of acid purple soil. Nitrogen fertilizer could raise lettuce soluble amino acid, crude protein and soluble sugar content and improved the quality of lettuce in acid pruple soil.