Effect of nickel (Ni) in the nutrient solution on yield, N metabolism, and nitrate content of leafy vegeta-bles is poorly understood. The aim of this nutrient solution culture experiment was to investigate the
effects of Ni supplementation on the nitrogen (N) metabolism and growth of lettuce (Lactuca sativaL. cv.
Baker) with either urea or nitrate as the N source. Nickel supplement at 0.04M reduced urea toxicity
to the urea-fed plants. Addition of Ni to the nutrient solution significantly increased the leaves and root
growth of the urea-fed lettuce plantswhile it increased the growth of lettuce plants fed with nitrate only
at N level of 20mM. At N level of 20mM, the leaves fresh weight of the urea-fed plants promoted by
Ni supplement was comparable with the nitrate-fed plants untreated with Ni. Nickel supplementation
increased the leaf total N concentrations in the urea-fed plants, although the nitrate-fed plants accu-mulated greater N in their leaves compared with urea treated plants at without Ni treatment. Nickel
addition decreased the concentrations of leaf urea-N in the urea-fed plants and NO3-N in the nitrate-fed
plants. Nickel addition enhanced urease activity in the leaves of urea-fed plants. The results indicated Ni
supplementation enhances the growth of the urea-fed lettuce plants while it has role in decreasing leaf
nitrate concentration and thus, improving the health quality of the nitrate-fed plant