The effect of organic manure and inorganic fertilizer on soil aggregate size distribution and stability, and associated carbon (C) within aggregates varies greatly in previous studies because of the differences in soil conditions, cropping systems, and management practices. This study was conducted as two field fertilization experiments, with different cropping systems, under a subtropical climate in China. The two field experiment sites were located in Jinhua (established in April 2011) in the Jinqu basin in Zhejiang province and Jintan (established in October 2010) in the low-middle Yangtze River plain in Jiangsu province. Both experiments consisted of four treatments, including unfertilized (CK), mineral fertilizer nitrogen (N)–phosphorus (P)–potassium (K) (NPK), NPK plus straw (NPK + SR), and NPK plus cattle manure (NPK + FYM) or half NPK plus cattle manure (1/2NPK + FYM). Water stable aggregate size classes (>5, 2–5, 1–2, 0.5–1, 0.25–0.5, and 0.25 mm were also determined. The results showed that aggregate-size distribution varied with soil types. Combined application of NPK and organic matter (straw residue or cattle manure), unlike the CK and NPK treatments, significantly increased the WSA >0.25 mm, MWD, and GMD, while obviously reducing the proportion of 0.25 mm, MWD, GMD, and associated C were observed between CK and NPK at both sites. The addition of FYM to the NPK treatment yielded the highest SOC contents in bulk soil, and showed significantly higher associations of C within all size aggregates at both sites. In contrast, NPK + SR significantly increased SOC within aggregate classes (2–5 mm, 0.5–1 mm, 0.25–0.5 mm, and 5 mm and 1–2 mm) at Jintan compared to the CK and NPK treatments. Overall, the combined application of FYM and mineral NPK was the best sustainable management practice for the improvement of aggregate stability and SOC sequestration.

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 (C) and nitrogen (N) 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). Although higher fertilizer costs were in the CRF + CM treatments, one-time application could save labor costs compared to the conventional split application of chemical fertilizers. The results showed that, compared to the NPK alone, the combined application of NPK with organic amendments improved the proportion of >0.25 mm macroaggregate, soil organic carbon (SOC), total nitrogen (TN) concentrations, and mean weight diameter (MWD) in both rhizosphere and bulk soil during the whole rice growing season. In rhizosphere, the proportion of macroaggregate was significantly positively (p < 0.01) correlated with root biomass while it had no significant correlation with SOC in the proportion of all sizes of 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-sized aggregates (0.25–2 mm and <0.25 mm). In addition, the organic C associated with 0.25–2 mm showed the largest contribution of the total SOC content in all treatments during the rice growing stage. Overall, the results suggested that the medium-term application of mineral fertilizer with organic amendments was beneficial to improve soil aggregate stability and C and N accumulation.

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