Medium-term Effects of Mineral Fertilizer and Organic Amendments on Aggregate and Soil Organic Carbon and Nitrogen Dynamics in Rhizosphere and Bulk Soil

Abstract Soil aggregate stability is one of the important physical properties affecting rice ( Oryza sativa L.) production and soil sustainability. This study was undertaken to evaluate the influence of different medium-term fertilization regimes on soil aggregate stability and aggregate associated carbon and nitrogen in rhizosphere and bulk soil. This experiment consisted of three treatments including mineral fertilizer alone (NPK), mineral fertilizer plus rice straw (NPK + RS), and controlled-release blended fertilizer plus cattle manure (CRF + CM). The results showed that bulk soil contained higher mean weight diameter (MWD) than in rhizosphere soil at the rice jointing and maturity stages. Compared to the NPK alone, combined application of NPK with organic amendments improved the proportion of > 0.25 mm macroaggregate, soil organic carbon (SOC), total nitrogen (TN) concentrations, and MWD in both rhizosphere and bulk soil. In rhizosphere, the proportion of macroaggregate was significantly positively ( p < 0.01) correlated with root biomass while had no significant correlations with SOC in all sizes aggregates. By contrast, bulk soil had a significantly ( p < 0.01) positive relationship between the proportion of > 2 mm class and organic C associated with smaller particle-size aggregates (0.25–2 mm and < 0.25 mm). During the rice-growing season, the highest MWD value was observed at the jointing stage except for the NPK + RS treatment in bulk soil. Overall, the results suggested that the medium-term application of mineral fertilizer with organic amendments is beneficial to improve soil aggregate stability and C and N accumulation.