In order to improving yield of vegetables, too many fertilizers are applied, especially nitrogen (N) and phosphate (P) fertilizers. The large number of nitrogen fertilizer lead to nitrate accumulation in vegetables. N and P nutrient loses heavily to lead to soil and water pollution due to short growth cycle in vegetable and the low fertilizer use efficiency. Furthermore, it is well known that high dietary intake of nitrate and nitrite in foods can be hazardous to human health and causes cyanosis.

Plant growth regulator effected many aspects in plant growth processes. In order to investigate the effect of plant growth regulators on the biomass, nitrate accumulation, N, P, K absorption and utilization in leafy vegetable, the lettuce was treated with three plant growth regulators (IAA, 6-BA and GA3) by adding or not adding vitamin B1 or Vc. Results showed that the biomass of lettuce increased significantly, meanwhile the nitrate content significantly reduced in condition of 50% conventional fertilization (CF) by spraying different plant growth regulators. Compared with only application of 50% CF, spraying plant growth regulators can improved soil nutrient availability, especially soil nitrate and enhanced N, P, and K absorption by plant. Consequently, the content of total N, P, and K in lettuce was improved greatly and the nutrient accumulation was significantly increased, too. Factor analysis of variance showed the influence degree of IAA, GA, 6-BA, VB1 and VC on lettuce biomass was: 6-BA>IAA>VB1≈GA3; on nitrate accumulation was: GA3>IAA>VB1>6-BA; on nitrate concentration in soil was: IAA>6-BA>GA3>VC. Considering the primary and second factors, the optimum combination of plant growth regulator was 6μM IAA，2μM 6-BA，0.5μM GA3, 150μM VB1 for the lettuce in condition of 1/2 CF.

These results will be published on Journal of the Science of Food and Agriculture.