Vermicompost as a soil supplement to improve growth, yield and quality of lettuce (Lactuca saliva L.)

The effects of earthworm-processed cattle-manure (vermicompost) on the growth, productivity and quality characteristics of five lettuce (Lactuca sativa L.) cultivars, were investigated in greenhouse experiments during two successive crop seasons (winter and spring season). Four treatments were applied, vermicompost combined with soil in proportions of 10 and 20% (w/w), inorganic fertilization and control (unamended soil without fertilization). Addition of vermicompost, in both concentrations, affected leaf biomass in all cultivars with leaf fresh weight to be significantly greater than in the control and the inorganic fertilization treatment during the winter crop season, whereas the lettuce yield in the higher vermicompost treatment was greater and close to the inorganic fertilization yield during the spring cultivation. Leaf number and leaf dry weight were significantly affected with the addition of vermicompost compared with the control and inorganic fertilization treatments during the winter cultivation whereas root biomass was significantly increased in the vermicompost treatments with the differences to be greater during the spring crop season. Photosynthetic rate did not differ significantly with the addition of vermicompost compared with the inorganic fertilization but was greater than in the control mainly in the spring experiment. Total chlorophyll concentration was increased in the two vermicompost treatments compared with the control in both cultivations. The addition of 20% vermicompost in the soil resulted in significantly higher chlorophyll levels than the inorganic fertilization but only during the winter crop season. Ascorbic acid concentration was affected by genotype but no significant differences were shown with the addition of vermicompost. The highest nitrate concentration for all lettuce cultivars was observed during the winter crop season with significantly greater levels (460-583 mg kg(-1) FW) in the inorganic fertilization treatment in both crop seasons.