Dataset for research entitled "Hydrochar as a potential soil conditioner for mitigating H⁺ production in the nitrogen cycle: A comparative study"

In this study, we investigated how rice-straw hydrochar would affect soil nitrification and nitrate leaching. We (1) determined how hydrochar addition interferes with nitrification mediated by soil microbes;(2) verified whether hydrochar input notably reduces nitrate leaching risks; and (3) elucidated the possible mechanisms by which hydrochar impacts soil nitrification and nitrate leaching relative to pyrochar.Our results showed that hydrochar addition mitigated the net nitrification rate by 3.75%~48.75% and 57.92%~78.19%, respectively, in contrast to the control and pyrochar treatments. This occurred mainly because a greater amount of dissolved organic carbon (DOC) was released from hydrochar (148.42 mg kg^-1~255.58 mg kg^-1) than the other treatments (117.13 mg kg^-1~122.22 mg kg^-1), which stimulated greater microbial nitrogen immobilization.The abundances of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were dramatically elevated by 25.62%~153.19% and 12.38%-22.39%, respectively, in the hydrochar treatments because of DOC-driven stimulation. The cumulative leaching loss of NO₃^--N in soils amended with hydrochar was markedly reduced by 43.78%~59.91% and 61.70%~72.82% compared with that in the control and pyrochar treatments, respectively, becausehydrochar promoted the soil water holding capacity by 2.70%~9.04% and reduced the residual NO₃^--N content by 20.36%~36.21%.Collectively, we highlighted that (1) Hydrochar addition mitigated the increase in net H⁺production resulting from soil nitrification and the NO₃^--N leaching process; (2) Hydrochar can decrease the soil nitrification rate by providing abundant DOC and enhancing microbial nitrogen immobilization; (3) The promoting effect of soil nitrification caused by increased AOA and AOB abundance might be neutralized by intensive NH₄⁺-N assimilation in hydrochar-amended soils; (4) Hydrochar decreased the risk of NO₃^--N loss via leaching, as it promoted soil saturated water-holding capacity and reduced NO₃^--N content. A graphical abstract was also provided below to help understand the framework and results of this work.