Fixation of ammonium-N from fertilizer by soil clay minerals and its subsequent release is of significance in regulating soil N supply for plants, preventing N losses, and improving fertilizer N use efficiency. Taking a black soil from Jilin of Northeast China as the test soil, a pot experiment consecutively cropped with spring wheat-buckwheat-spring wheat was conducted, aimed to evaluate the effects of different ( 15 NH 4 ) 2 SO 4 fertilization practice on the amount and subsequent release of soil recently fixed fertilizer 15 NH 4 + in the test soil over the consecutive crop cultivation. 19.60-30.88% of applied 15 NH 4 + -N was fixed after 10 days of fertilization, suggesting that the black soil had a higher potential of fixing fertilizer NH 4 + -N. During the consecutive crop cultivation of spring wheat-buckwheat-spring wheat, an average of 80.95%, 7.13% and 2.27% of soil recently fixed 15 NH 4 + -N was released in the first, second, and third crop cultivation, respectively. This indicates that the release of soil recently fixed fertilizer NH 4 + -N is a relatively long-term process, and it was quite active in the early period of fixation and easily utilized by the first crop cultivation. High N application rate increased significantly the fixation and release of applied 15 NH 4 +-N (P