Objective The combined effects of biochar and urease/nitrification inhibitors on soil acidification and nitrification were studied, to provide a theoretical basis for the amelioration of acidified soils with biochar.

Methods A laboratory soil incubation experiment was carried out. An acidic vegetable soil selected from a long-term over-fertilized vegetable production field was used as the research object. The biochar derived from spent mushroom substrate of Pleurotus eryngii cultivation, combined with urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and/or nitrification inhibitor 3,4-dimethylpyrazol-phosphate (DMPP) were added to the soils with urea application, to investigate the effects of their combined application on the contentsof soil ammonium nitrogen (AN), nitrate nitrogen(NN), inorganic nitrogen (IN), as well as apparent nitrification rate (ANR), nitrification inhibition rate (NIR) and pH value.

Results In acidified soil, compared with urea applied alone, the AN contents were increased while the NN contents were decreased in the treatments of urea combined with nitrogen inhibitors, and the soil pH values were increased by 0.03–0.45 units at the end of incubation stage., whereas soil acidification induced by nitrogen application can only be alleviated by inhibitors. In contrast, the final soil pH values were significantly increased by 0.99–1.10 units (P ＜ 0.05) with biochars applicaiton, and obvious ameliorative effects on acidified soil are achieved, the ANR was also increased significantly by 13.53%–52.48% (P ＜ 0.05) after 28 days of incubation, raising the risk of soil nitrogen loss. Compared with urea combined with biochar, the soil pH value was elevated when co-application of biochar with inhibitors while modulating soil nitrogen transformation. The NIR of treatments containing DMPP remained positive value in the first 42 days of incubation, and the highest NIR was achieved in the treat of biochar with two inhibitors.

Conclusion The pH value was effectively increased while soil nitrogen transformation was regulated by the co-application of biochar with nitrogen inhibitors, among which the best effect was found in the treatment of combined application of biochar with urease/nitrification inhibitors.