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In order to reveal the residual situation of fertilizer nitrogen in paddy soil under water and biochar management, the method of combining field plot experiment with micro-plot was used to label basal fertilizer, tillering fertilizer and panicle fertilizer respectively. Compared with traditional flooding irrigation, the residual situation of basal fertilizer, tillering fertilizer, panicle fertilizer and whole fertilizer in paddy soil after rice harvest and the distribution law of nitrogen residue in different depths soil layer of fertilizer applied at different stages under different water and biochar management modes were studied. The results showed that the total nitrogen residues in paddy soils under different biochar application levels was 28.16%~34.42% under dry-wet-shallow irrigation mode, and the nitrogen residues of basal fertilizer, tillering fertilizer and panicle fertilizer were 27.53%~41.35%, 34.32%~43.50% and 11.58%~25.67%, respectively. When the application amount of biochar was below 12.5t/hm2, the residual amount of basal fertilizer and tillering nitrogen in paddy soil was increased with the increase of biochar application amount under the two irrigation modes after harvest, while the residual amount of panicle fertilizer nitrogen in paddy soil was decreased with the increase of biochar application amount. Under the same application level of biochar, the residual rate of fertilizer nitrogen in soil was significantly higher than that in conventional flooding irrigation (P<0.05), the residual amount of fertilizer nitrogen in the same soil depth under the same biochar application level was significantly different between the two irrigation modes (P<0.05). The residual amount of nitrogen fertilizer applied at different stages under different biochar application levels in paddy field under dry-wet-shallow irrigation mode was higher than that under conventional flooding irrigation, while the residual amount in 40~60cm soil layer was lower than that under conventional flooding irrigation. And the application of biochar as 25t/hm2 had a negative effect on the residual nitrogen of basal fertilizer, tillering fertilizer and panicle fertilizer in paddy soil under dry-shallow-wet irrigation mode. Reasonable water and biochar management model can increase the residual amount of fertilizer nitrogen in plough soil (0~20cm), reduce the loss of fertilizer nitrogen, inhibit the movement of fertilizer nitrogen to deep soil, and reduce the risk of pollution of fertilizer nitrogen residue in soil to paddy ecological environment. The results can provide theoretical basis and technical support for the application of water and carbon management model in paddy field in cold and black soil region.