Effects of several new-type compound fertilizers on the quality of romaine lettuce cultivated soillessly

A pot culture with the soil-less medium, i.e. the mixture of three solid materials (pearlite: coal cinder: sand=50:100:190), was conducted to study the effects of three new-type compound fertilizers on the yield, the contents of nitrate, heavy metal and nutrient quality of romaine lettuce. Results indicate that the yields of romaine lettuce under different treatments vary significantly and the fertilizers is in the order of organic-inorganic compound fertilizer＞bio-compound fertilizer＞inorganic nutrient solution (check)＞organic compound fertilizer according to the yield of lettuce with different fertilization. The contents of nitrate of romaine lettuce range from 1375mg/kg to 3935mg/kg and the maximum of nitrate appears in the check and the minimum in the organic-inorganic compound fertilizer treatment. Three compound fertilizers can reduce the nitrate contents of romaine lettuce by 37.9%～72.5% as compared with the check. Contents of Hg, Pb and Cr in romaine lettuce under three compound fertilizer treatments are lower than GB (the national limit indices of China) and reduced by 20.8%～83.1% as compared with the check. Total accumulations of Hg, Pb, and Cr in romaine lettuce account for 11.1%～63.0%，38.2%～78.7% and 10.9%～53.5%, respectively, under the compound fertilizer treatments. Applying compound fertilizer can obviously improve soluble sugar and Vc contents, but a different effect on the content of amino acid in romaine lettuce is observed.