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.