Conservation tillage (CS) is a major component of sustainable soil management. The objective of the study was to investigate soil C and N pools and the associated microbial activities in sandy Ultisols after 40 yr of CS and conventional tillage (CT). Soil samples were collected from fields under continuous CS and CT for 40 yr (1979–2018) and subjected to a range of physio-biogeochemical analyses. When compared with CT, CS increased total C, total N, and active C by 35, 45, and 44% at 0-to-5-cm depth, respectively, but not at 5-to-15-cm depth. In contrast, CT had 128 and 121% higher inorganic N and dissolved organic N at 5-to-15-cm depth, which was not observed at 0-to-5-cm depth. Respiratory CO₂ production and organic N mineralization were found to be higher in CS soils than in CT soils at 0–5 cm, but both were higher in CT than CS at 5–15 cm. Concurrently with increased active C concentrations, potential activities of C-cycling enzymes were higher in CS soils than CT soils at 0–5 cm, which was not observed at 5–15 cm. The increased labile C supply stimulated microbial activities in CS soils at 0–5 cm, but at 5–15 cm, the higher N availability increased microbial biomass N and organic N mineralization potentials in CT than CS soils. The contrasting CS and CT impacts on C and N at different soil depths likely reflected the decouple of C and N cycling in the tested soils.

中文翻译：

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对比不同土壤深度耕作对碳和氮的反应：40 年耕作管理后的观察

保护性耕作 (CS) 是可持续土壤管理的主要组成部分。该研究的目的是调查土壤 C 和 N 库以及在 40 年的 CS 和常规耕作 (CT) 后沙质 Ultisol 中的相关微生物活动。在连续 CS 和 CT 下从田间收集土壤样品 40 年（1979-2018 年），并进行了一系列物理-生物地球化学分析。与 CT 相比，CS 在 0 到 5 厘米深度处分别使总碳、总氮和活性碳增加了 35%、45% 和 44%，但在 5 到 15 厘米深度处则不然。相比之下，CT 在 5 至 15 厘米深度处的无机氮和溶解有机氮分别高出 128% 和 121%，而这在 0 至 5 厘米深度处没有观察到。呼吸 CO ₂发现在 0-5 cm 处，CS 土壤中的产量和有机氮矿化高于 CT 土壤，但在 5-15 cm 处 CT 均高于 CS。在活性碳浓度增加的同时，CS 土壤中碳循环酶的潜在活性在 0-5 cm 处高于 CT 土壤，而在 5-15 cm 处未观察到。增加的不稳定碳供应刺激了 CS 土壤中 0-5 cm 处的微生物活动，但在 5-15 cm 处，与 CS 土壤相比，更高的 N 可用性增加了 CT 中微生物生物量 N 和有机 N 矿化潜力。CS 和 CT 在不同土壤深度对 C 和 N 的对比影响可能反映了测试土壤中 C 和 N 循环的解耦。