In central Jilin a ¹⁵N micro-plot experiment was conducted in a piece of farmland of black soil to study ef ect of the depth and frequency of N application on utilization rate of N fertilizer.Results show that the treatment of sidedressing twice at a depth of 10~15cm increased the rate from 24.5% in the CK,the traditional once for all shallow sidedressing on the ridge,to 39.0%,clearly indicating that deep and split application of N fert ilizer improves utilization rate.The total fertilizer N loss was 16%~27%;N residual in the soil 34%~54%;about half of the ¹⁵N labeled fertilizer was taken up by maize during the grain-forming period after Aug.1;70%~90% of the loss occurred within the 35 days after the N fertilizer was sidedressed;and crop response to the application was not significant.