Effects of different proportions of N，P，and K on nitrate contents in rape

The field and plot experiments were conducted to study the effect on the accumulation of nitrate in rape by applying different kinds of fertilizers and proportions． The results show that nitrogen fertilizer is the main source of the NO₃^--N in rape．The appropriate combination of N ，P，and K fertilizer can significantly reduce the NO₃^--N content，and there are big differences in the effect on nitrate by applying different N，P，and K proportions in field and greenhouse conditions．The best amounts of N，P，and K applied in greenhouse is N 225kg／hm²，P₂0₅ 60kg／hm²，and K₂O₄5kg／hm²，and the proportion of N：P₂0₅：K₂O is 5：1．33：1．In this way the guaranteed high yield and low nitrate in rape can be obtained．