Effects of localized deep placement of paste-like fertilizer on the growth and quality of lettuce (Lactuca sativa L. var. crispa)

To evaluate the effect of localized deep placement of paste-like fertilizer, the growth and quality of lettuce (Lactuca sativa L. var. crispa) were examined in potted plants receiving different application rates of paste-like fertilizer, compared to standard fertilization using a compound fertilizer (standard, N, P2O5 and K2O applied to the soil at a rate of 120 mg kgE-1 respectively). When the paste-like fertilizer was applied at a rate that was 20-30% less than the standard, the dry matter production of lettuce could be comparable to that for the standard treatment. The content of red color tone, anthocyanin and Brix soluble solids in lettuce grown with paste-like fertilizer treatment applied at a 20-30% reduction rate was higher than that in lettuce grown with standard treatment, while the nitrate content was lower than that in plants grown with standard treatment. Therefore, these results suggested that localized deep placement of paste-like fertilizer might improve the quality of lettuce and reduce the rate of fertilizer application. When four kinds of fertilizer, i.e. compound fertilizer, paste-like fertilizer, coated fertilizer and rapeseed cake, were applied as side dressing treatment at a rate 20% less than the standard treatment in the container experiment, N uptake by lettuce receiving the side dressing treatments did not significantly differ from that in the standard treatment irrespective of the kinds of fertilizer. However, the nitrate content in lettuce grown with the side dressing treatment was lower than that in plants grown with the standard treatment. This tendency was especially remarkable with coated fertilizer and rapeseed cake treatments. The soil applied as side dressing promoted delayed nitrification; therefore it was considered that the reason for the decrease in nitrate in lettuce grown with side dressing treatment, especially coated fertilizer and rapeseed cake, was that the rate of nitrate uptake was relatively decreased, while that of other nitrogen forms, mainly ammonium, was increased.