Vegetable is the crop which can easily enrich nitrate.In order to obtain a high yield of vegetable,farmers now excessively apply chemical nitrogenous fertilizer,thus resulting in a drastic increase in nitrate accumulation and vegetable quality deteriorated.In our study two kinds of fertilizers,ammonium chloride NH 4Cl and ammonium sulphate (NH 4) 2SO 4 were selected for correlation.It was proposed to apply N.fertilizer at a dose of 300kg/hm 2 as critical proper level to set a safe initial period adequ...