The effects of rainfall intensity(RI) and rain-fertilization interval(RFI) on N export by runoff in oilseed rape land were studied with simulated rainfall and in situ soil pot experiment.The tested soil was collected from the surface layer(0~20 cm) of cole field

in Jiaxing city

Zhejiang province in Southeast China.Our results show that: firstly

N concentrations in runoff increase with the increase of RI and decrease with the increase of RFI.The process of N export by runoff can be separated into two steps

i.e.

fluctuation step and stable step

and there is a high loss risk for N in the fluctuation step.Nitrate-N is the predominant N form in runoff

with the ratio of nitrate-N/TN more than 0.3 in all treatment.This study indicates that high RI and short RFI would enhance N loss by runoff greatly

and suggested that fertilization should be taken at RFI>5~7 days

so that N loss by runoff could be largely mitigated.