Introduction Nitrogen is one of the main elements in the nutrient solution. In general plants are able to absorp and metabolize both NO_3 and NH_4, but NO_3 should be the main nitrogen form used in the nutrient solution because high level of NH_4 will cause NH_4 toxicity, resulting in lower tissue Ca and Mg concentration, incidence of blossom-end rot(BER). Many studies indicate that the growth of vegetables supplied with NO_3+NH_4
