Abstract: Taking the Napplication rate, method and main varieties applied in paddy field of black soil in Northeast China as the parameters, a micro-plot tracer isotope trial and a normal urea plot trial were conducted for two years to study the fate of fertilizer nitrogen in paddy field. The results showed that 22.2%～46.1% of applied chemical fertilizer nitrogen was absorbed and remained in the paddy plant, and averaged 37.68%. About 12.7% to 25.4 % of applied N during the same year was remained in the soil. The determined nitrogen losses rate through ammonia volatilization in a closed chamber system was 19.0%～44.2%. The use efficiency of chemical fertilizer N was influenced by the application method. Higher use efficiency would be obtained with deeper or mixing application method. The amount of nitrogen remained in soil were related to the application method, and the remained rate was increased with the amount and application depth increasing. The experiment with ¹⁵ showed that no ¹⁵N residue was detected below 80cm in depth, which was because the heavy texture of the black soil. The results of the tracer isotope trial and the plot experiments showed that there was a rough balance between the amount of residual nitrogen in soil and the priming effect from chemical fertilizer nitrogen.

Key words: Black soil region, Paddy field, Fertilizer nitrogen