Abstract: Abstract: Excessive application of nitrogen fertilizer in agricultural soils is considered as a main cause of ecological problems such as nitrogen leaching, which has become an important limitation to improving nitrogen use efficiency in agricultural production. Because of its physical, chemical, and biological stability, biochar when applied to soils can play a key role in nutrient cycling, potentially affecting nitrogen retention and improving soil fertility. However, experimental results were variable and dependent on the experimental set-up, soil properties, and fertilizer application rates and biochar were set up at the high and low levels, which possess a big blind area. A laboratory experiment was conducted to investigate the effects of biochar additions on dynamic changes of nitrogen under artificial rainfall conditions by adding 0, 0.5%, 2%, 4%, 6%, and 8% biochar (the biochar was prepared by pyrolyzing corn straw at 500-550℃ under oxygen limited condition) into soil columns collected from red dryland of southern China under urea application condition (300 kg/hm2). The results showed that the speed of leaching of NO3- and total nitrogen was delayed by biochar applications. Compared with urea application treatment, the total nitrogen and NH4+ contents in leachate were significantly decreased by 4.02% and 8.93% when ≥2% biochar was applied into soil, and the NO3- contents of leachate was obviously decreased by 3.23%-11.87% when the biochar ratio reached 4%. But there was no significant effect of adding small amount of biochar (such as 0.5%) on N leaching compared with urea application treatment. Leaching losses of NO3- had been found to be highest because the NO3- was mobile, and may not be taken up by plants. NO3- leaching amount accounted for 84%-90% of the total nitrogen leaching amount, while NH4+ leaching only accounted for 0.4%-2%; The total nitrogen content of different soil layers in each treatment was similar regardless of the fertilization and biochar applications. While the total nitrogen contents in soils were markedly different among the treatments. Compared with urea application treatment, the content of soil total nitrogen was significantly increased by 4.62% to 10.62% when biochar addition was ≥2%, and the relationship between addition amounts of biochar (x) and the content of soil total nitrogen (y) followed an index equation: y=1.6e0.0845x (R2=0.99, n=24). The results above suggested that biochar could be used as a potential additive for nutrient retention in order to increase the utilization efficiency of chemical fertilizers. In conclusion, biochar additions could decrease the leaching amount of NH4+, NO3- and total nitrogen and partly increased the concentration of soil total nitrogen. However, the low biochar addition had no significant effects on reducing nitrogen leaching and increasing soil total nitrogen content. Therefore, the purpose to obviously decrease nitrogen leaching and increase the content of soil total nitrogen could be realized only when biochar addition was above 2% in dryland soil. Nonetheless, the effect of biochar addition on reducing soil nitrogen leaching needs to be further verified before biochar can be applied to agricultural fields on a large scale.