Fixation of labeled (15NH4)2SO4 and its subsequent release in black soil of Northeast China over consecutive crop cultivation

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 (15NH4)2SO4 fertilization practice on the amount and subsequent release of soil recently fixed fertilizer 15NH4+ in the test soil over the consecutive crop cultivation. 19.60–30.88% of applied 15NH4+-N was fixed after 10 days of fertilization, suggesting that the black soil had a higher potential of fixing fertilizer NH4+-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 15NH4+-N was released in the first, second, and third crop cultivation, respectively. This indicates that the release of soil recently fixed fertilizer NH4+-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 15NH4+-N (P < 0.01). To improve the use efficiency of ammonium fertilizers in the crop production of black soil in Northeast China, the soil recently fixed fertilizer NH4+ should be taken into account when an advanced nitrogen management strategy was to be developed.