The global soil carbon pool comprises soil organic carbon (SOC), found in almost all soils, and soil inorganic carbon (SIC), in calcareous soils. Despite their agricultural significance, calcareous soils, which exhibit diverse chemical properties and are found in varied environments, have historically been understudied. Using soils obtained from a decade-long, fully factorial field experiment located on temperate, near neutral pH, calcareous soils, this study examined the influence of cover crops (no-cover vs radish) and three levels of tillage intensity: shallow (10 cm) and deep (20 cm) non-inversion, and plough (25 cm inversion) on SOC and SIC stocks. Further, considering recent experimental and observational evidence indicating the interactions of SOC and SIC pools and their likely microbial control, we also investigated how SOC, the soil microbial biomass pool, and SIC are correlated. For SOC stock, there were significant interactions with total SIC and SOC:SIC ratio that differed by tillage intensity. Across the whole soil profile (0–60 cm), there was a significantly positive relationship between SOC content and SIC stock that was only present with ploughing. Further, at low SOC:SIC ratios (∼0.5–3.0), while SOC stock was marginally lower under plough, at higher SOC:SIC ratios (∼3.1–10.0), SOC stock was predicted to be up to ∼4–fold greater (4 kg m−2) with ploughing than the lower intensity tillage treatments. This result highlights a critical SOC-SIC interaction that, depending on tillage intensity, may offset anticipated disturbance-related loss of SOC, and challenges the common perception that tillage consistently reduces SOC. SOC stock was also ∼40 % (0.42 kg m−2) greater at 0–10 cm and ∼30 % (0.2 kg m−2) greater at 30–40 cm under radish cover crop than without. SIC stock differences were correlated with SOC content, tillage intensity and cover cropping. SIC stock was strongly correlated with SOC, with a predicted ∼0.3–1 kg m−2 increase in SIC stock for ∼1 % increase in SOC. Under radish cover crops and with ploughing, there was ∼0.7 kg m−2 more SIC than under all other conditions. Microbial biomass was positively correlated with SIC stock suggesting a causality that needs experimental testing. Given that reduced tillage is a frequently recommended practice to increase soil carbon storage and given the limited attention that has been paid to the influence of cover cropping on the SIC pool, our results indicate the need for further investigation around the dynamics of SOC and SIC interactions and stabilization processes in calcareous soils and highlights the pitfalls of a one-size-fits-all approach to soil carbon management.

中文翻译：

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耕作和覆盖作物下的土壤有机碳和无机碳相互作用决定了温带石灰质土壤中碳积累的可能性


全球土壤碳库包括几乎所有土壤中的土壤有机碳 （SOC） 和石灰质土壤中的土壤无机碳 （SIC）。尽管石灰质土壤具有农业意义，但它们表现出不同的化学性质并在不同的环境中发现，历来研究不足。本研究使用从温带、接近中性 pH 值、石灰质土壤上进行的长达十年的全因子田间试验中获得的土壤，检查了覆盖作物（无覆盖与萝卜）和三个耕作强度级别的影响：浅 （10 cm） 和深 （20 cm） 非倒置，以及犁（25 cm 倒置）对 SOC 和 SIC 存量的影响。此外，考虑到最近的实验和观察证据表明 SOC 和 SIC 库的相互作用及其可能的微生物控制，我们还研究了 SOC、土壤微生物量库和 SIC 是如何关联的。对于 SOC 存量，与总 SIC 和 SOC：SIC 比率存在显著交互作用，这些比率因耕作强度而异。在整个土壤剖面 （0–60 cm） 中，SOC 含量与 SIC 存量之间存在显著的正相关关系，这仅在犁地中出现。此外，在低 SOC：SIC 比率 （∼0.5-3.0） 下，虽然犁下 SOC 存量略低，但在较高的 SOC：SIC 比率 （∼3.1-10.0） 下，预计犁地的 SOC 存量比低强度耕作处理高出 ∼4 倍 （4 kg m-2）。这一结果突出了关键的 SOC-SIC 相互作用，根据耕作强度，可能会抵消预期的与干扰相关的 SOC 损失，并挑战了耕作持续降低 SOC 的普遍看法。萝卜覆盖作物在 0-10 cm 处的 SOC 存量也比没有萝卜覆盖作物时高 ∼40 % （0.42 kg m-2），在 30-40 cm 处比没有萝卜覆盖作物时高 ∼30 % （0.2 kg m-2）。 SIC 存量差异与 SOC 含量、耕作强度和覆盖作物相关。SIC 储量与 SOC 密切相关，预计 SOC 增加 ∼0.3 – 1 kg m-2 的 SIC 储量会增加 ∼1 %。在萝卜覆盖作物和犁地下，SIC 比所有其他条件下高出 ∼0.7 kg m-2。微生物生物量与 SIC 存量呈正相关，表明存在需要实验测试的因果关系。鉴于减少耕作是增加土壤碳储存的一种经常推荐的做法，并且鉴于对覆盖作物对 SIC 池的影响的关注有限，我们的结果表明需要进一步研究石灰质土壤中 SOC 和 SIC 相互作用和稳定过程的动态，并强调了一刀切的土壤碳管理方法的陷阱。