Effects of Organic Manure on Nitrate Accumulation in Soil-Cucumber System Under Protected Cultivation Condition

A field experiment with cucumber plant was conducted under protected cultivation condition to study the effects of different appli-cation rates( 0￣60 t·hm-2) of organic manure on the accumulation characteristics of nitrate( NO3-- N) in soil- cucumber system. The results showed that the accumulation characteristics of NO3-- N in soil and cucumber plant were affected by the growth stage of cucumber and the ap- plication rate of organic manure. At vigorous fruiting stage, the NO3-- N content in 0￣40 cm soil layer was higher than that at earlier and later growth stages, and in cucumber plant comprising lamina and cucumber the NO3- - N content was also higher than that at earlier and later growth stages. When the application rate of organic manure was 60 t·hm-2 at vigorous fruiting stage, the NO3-- N content in 0￣40 cm soil layer was the highest, and the NO3-- N content in the lamina of cucumber was the highest. Cucumber at its vigorous growth stage with 60 t·hm-2 application rate of organic manure was surpassed the standard of China foodstuff security( 410 mg·kg-1) . When the application rate of organic manure was less than 20 t·hm-2, nosignificant NO3--Naccumulation was observed in soil, and so did the lamina of cucumber, and the NO3--N content in cucumber at its various growth stages was not surpassed the standard of China foodstuff security( 410 mg·kg-1) . It was suggested that appropriate application rate of organic manure could not result in an over-accumulation of NO_(3-)-Nin soil-cucumber system.