Carbon (C) sequestration in soil is limited by the soil’s maximum C carrying capacity (C_m) and C saturation deficit (S_d). These two parameters have enormous implication for choosing appropriate management strategies to increase a soil’s C sequestration potential (CSP). The present study aims to estimate the C_m and S_d of two Alfisols from Bhubaneswar (Alfisol-BHNS) and Pattambi (Alfisol-PTMB) and two Vertisols from Parbhani (Vertisol-PRBN) and Junagadh (Vertisol-JNGD) in India with a history of long-term manuring and fertilization practices. Both the Alfisols maintained a rice-rice cropping system whereas the Vertisols had a soybean-safflower and groundnut-wheat cropping system, respectively. Irrespective of soil types and cropping systems, the soil organic C (SOC) content and stock were the highest in the treatment receiving 100% of recommended dose of NPK combined with 10 Mg ha^-1 well decomposed farmyard manure (100%NPK+FYM). The mean annual estimated return of C (MAERC) across the soil types followed the order 100%NPK + FYM> 150%NPK = 100%NPK +Lime (Agricultural grade, purity 80%)> 100%NPK > 50%NPK > control. The C_m at 0–30 cm soil depth was 39.3, 21.7, 47.6 and 25.0 Mg ha^-1, respectively for Alfisol-PTMB, Alfisol-BHNS, Vertisol-JNGD and Vertisol-PRBN. The S_d value was the highest in the control treatment and lowest in100% NPK + FYM treatment, signifying a higher CSP of the former soil than the later. Therefore, 100%NPK +FYM treatment would require a minimum threshold level of C addition to maintain the SOC at equilibrium. The estimated minimum threshold limit of annual C input (A_E) to preserve the existing SOC level was 1.84, 0.39, 1.57 and 0.90 Mg ha^-1 yr^-1 for Alfisol-PTMB, Alfisol-BHNS, Vertisol-JNGD and Vertisol-PRBN, respectively. Alfisol-PTMB and Vertisol-JNGD showed a higher CSP than Alfisol-BHNS and Vertisol- JNGD because the former two soils had higher S_d values than the later soils. The MAERC, climate, soil texture and clay mineralogy largely influenced the SOC sequestration and C_m values. An integrated application of 100%NPK with either lime or FYM is recommended to maintain the sequestration and stabilization of SOC in the studied soils. The CSP of the soils could be further increased via innovative approaches such as increasing soil’s reactive mineral contents to lock additional C.

土壤中的碳 (C) 固存受到土壤最大碳承载能力 (C _m ) 和碳饱和亏缺 (S _d ) 的限制。这两个参数对于选择适当的管理策略来增加土壤的碳封存潜力（CSP）具有巨大的影响。本研究旨在估算来自印度布巴内斯瓦尔 (Alfisol-BHNS) 和 Pattambi (Alfisol-PTMB) 的两种 Alfisol 以及来自印度 Parbhani (Vertisol-PRBN) 和 Junagadh (Vertisol-JNGD)的两种Vertisol的 C _m和 S _d长期施肥和施肥的历史。两个 Alfisols 都维持水稻-水稻种植制度，而 Vertisols 则分别采用大豆-红花和花生-小麦种植制度。^{不论土壤类型和种植制度，土壤有机碳（SOC）含量和储量以100%推荐剂量NPK配合10 Mg ha -1}腐熟农家肥（100%NPK+FYM）处理最高。。不同土壤类型的平均年估计碳回报率 (MAERC) 的顺序为 100%NPK + FYM> 150%NPK = 100%NPK +石灰（农业级，纯度 80%）> 100%NPK > 50%NPK > 对照。Alfisol-PTMB、Alfisol-BHNS、Vertisol-JNGD 和 Vertisol-PRBN 在 0-30 cm 土壤深度的C _m分别为 39.3、21.7、47.6 和 25.0 Mg ha ^-1。S _d值在对照处理中最高，在100% NPK + FYM 处理中最低，表明前者的CSP 高于后者。因此，100%NPK +FYM 处理需要添加最低阈值水平的 C，以维持 SOC 平衡。对于 Alfisol-PTMB、Alfisol-BHNS、Vertisol-JNGD 和 Vertisol-PRBN，维持现有 SOC 水平的年度碳输入 (A _{E )}估计最低阈值为1.84、0.39、1.57 和 0.90 Mg ha ^-1 yr ^-1， 分别。Alfisol-PTMB 和 Vertisol-JNGD 显示出比 Alfisol-BHNS 和 Vertisol-JNGD 更高的 CSP，因为前两种土壤的 S _d值高于后一种土壤。MAERC、气候、土壤质地和粘土矿物学在很大程度上影响了 SOC 固存和 C _m值。建议将 100%NPK 与石灰或 FYM 综合施用，以维持所研究土壤中 SOC 的封存和稳定。可以通过创新方法进一步提高土壤的 CSP，例如增加土壤的活性矿物质含量以锁定额外的 C。