Abstract: Modified biochar was studied as a soil additive in this paper to increase use efficiency of soil nitrate nitrogen (NO3-N) and available phosphorous (P) in soil profile,and reduce the leaching risk.The best modified condition for crop biochar were determined by laboratory experiment and the effect of modified biochar on leaching of soil NO3-N and available P was studied by soil column simulation test.The Fe3+ to biochar mass ratio of 0.7 was tested to be the best modified condition which would increase the absorption of NO3-N and available P greatlyModified biochar could absorb 12 more times of NO3-N and 66 more times of available P compared to unmodified biochar,in a KNO3 solution with 50mg·L-1 N concentration and a 50mg·L-1 P concentration KH2PO4 solution,the maximum amount of absorption was 2.47mg·g-1for NO3-N and 1658mg·g-1 for available P,respectively When 2.5%,5% and 10% of best modified biochar was added in soil,the NO3-N leakage was significantly reduced,by 20%,43% and 59% respectively compared to the control with no biochar addition. Available P leakage was also significantly decreased,by 45%,59% and 75% respectively.This study demonstrated that adding modified biochar in soil could effectively reduce NO3-N and P leakage in the soil profile.

Key words: Modified biochar, Nitrate nitrogen, Available phosphorus, Leaching