The paper studied the effects of applying 3 nitrification inhibitors,Hydroquinone(HQ),Dicyandiamide(DCD) and Thiourea(TU),on nitrate contents in soils and in pakchoi,yield and other nitrition qualities of pakchoi with plot experiment in 2 soils of suburb of Changsha city,Hunan Province,in 2002 and 2003.The results showed that all the nitrification inhibitors could decrease nitrate contents in soils and in pakchoi during the whole growth periods and increase the yield of pakchoi to some extent.But there were not the same tendency in different soils and for different nitrification inhibitors,the...