Impact of Dolomite Liming on Ammonia-Oxidizing Microbial Populations and Soil Biochemistry in Acidic Rice Paddy Soils

Background and Aims: Over the last few decades, rampant nitrogen fertilization has exacerbated soil acidification in agricultural ecosystems. To counteract this, liming has become an essential technique for rehabilitating fertility in acid-degraded agricultural soils. Our research aimed to shed light on the response of ammonia oxidizers to liming in acidic soils within a controlled rice paddy experiment. We conducted a pot experiment with rice, featuring three different treatments: a control with only soil, a low dolomite dose (LD), and a high dolomite dose (HD). Various soil properties were investigated throughout the study. Under flooding, soil pH values rose across the treatments, from 5.4 in the control to 6.8 in HD. Ammonium and nitrate levels peaked in the HD treatment, reaching 30 and 22 mg kg−1, respectively. Similarly, dissolved organic carbon and microbial biomass carbon surged at mid-season aeration, hitting highs of 101 and 30 mg kg−1, respectively, in the HD treatment. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) were responsive to dolomite-lime application, with distinct reactions; AOB abundance and potential nitrification rates were positively affected by higher lime doses, whereas AOA numbers decreased over time and with dolomite application. Additionally, soil enzymes such as urease, catalase, invertase, phenol oxidase, and phosphatase also increased progressively, mirroring the rise in soil pH. This study identified increased soil pH as the critical factor influencing various soil parameters, especially the balance between AOA and AOB populations. Both AOB and AOA were sensitive to liming; AOA decreased while liming stimulated AOB abundance.