The agricultural reuse of urban sewage sludge (USS) modifies soil properties depending on sludge quality, management, and pedo-environmental conditions. The aim of this microcosm study was to assess C mineralization and subsequent changes in soil properties after USS addition to two typical Mediterranean soils: sandy (Soil S) and sandy loam (Soil A) at equivalent field rates of 40 t ha-1 (USS-40) and 120 t ha-1 (USS-120). Outcomes proved the biodegradability of USS through immediate CO2 release inside incubation bottles in a dose-dependent manner. Accordingly, the highest rates of daily C emission were recorded with USS-120 (3.7 and 3.9 mg kg-1 d-1 for Soils S and A, respectively) after 84 d of incubation at 25 °C. The addition of USS also improved soil fertility by enhancing soil macronutrients, microbial proliferation, and protease activity. Protease showed significant correlation with N, total organic C, and heterotrophic bacteria, reflecting the biostimulation and bioaugmentation effects of sludge. Soil indices like C/N/P stoichiometry and metabolic quotient (qCO2 ) varied mostly with mineralization rates of C and P in both soils. Despite a significant increase of soil salinity and total heavy metal content (lead, nickel, zinc, and copper) with USS dose, wheat germination was not affected by these changes. Both experimental soils showed intrinsic (Soil A) and incubation-induced (Soil S) phytotoxicities that were alleviated by USS addition. This was likely due to the enhancement of biodegradation and/or retention of phytotoxicants originating from previous land uses. Urban sewage sludge amendments could have applications in soil remediation by reducing the negative effects of allelopathic and/or anthropogenic phytoinhibitors.

中文翻译：

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碳矿化、生物指标和植物毒性评估城市污水污泥对两种轻质土壤的影响

城市污水污泥的农业再利用 (USS) 根据污泥质量、管理和土壤环境条件改变土壤特性。这项微观研究的目的是评估在 40 t ha-1 (USS) 的等效田间施用量下将 USS 添加到两种典型的地中海土壤：沙质（土壤 S）和沙质壤土（土壤 A）后 C 矿化和土壤性质的后续变化。 -40) 和 120 吨 ha-1 (USS-120)。结果证明了 USS 的生物降解性，通过在培养瓶内以剂量依赖性方式立即释放 CO2。因此，在 25 °C 下培养 84 天后，USS-120 记录的每日碳排放率最高（土壤 S 和 A 分别为 3.7 和 3.9 mg kg-1 d-1）。添加 USS 还通过增强土壤常量营养素、微生物增殖和蛋白酶活性来改善土壤肥力。蛋白酶与氮、总有机碳和异养菌呈显着相关，反映了污泥的生物刺激和生物强化作用。C/N/P 化学计量和代谢商数 (qCO2) 等土壤指数主要随两种土壤中 C 和 P 的矿化率而变化。尽管 USS 剂量使土壤盐分和总重金属含量（铅、镍、锌和铜）显着增加，但小麦发芽并未受到这些变化的影响。两种实验土壤都显示出内在的（土壤 A）和孵化诱导的（土壤 S）植物毒性，这些植物毒性通过添加 USS 得到缓解。这可能是由于生物降解的增强和/或来自先前土地用途的植物毒物的保留。