Sodic dispersive subsoils pose significant constraints to agricultural productivity and sustainability in arid and semiarid regions. Gypsum and organic amendments (OAs) have shown the potential to improve soil structure and fertility and may address constraints associated with these dispersive soils. However, the mechanistic linkages between the quality of OAs, and the dynamics of soil structural stability (i.e., soil aggregates), particularly under the interactive impacts of gypsum and exogenous nutrients, remain elusive. We quantified aggregate stability (i.e., wet mean weight diameter, WMWD) and the accumulation of OA-carbon (C) in different aggregate-classes in a dispersive clay subsoil (δ¹³C −24.5‰) with or without the application of OAs (δ¹³C −12.8 to −14.3‰), gypsum and/or exogenous nutrients (nitrogen (N) and phosphorus (P)) over the 270 days incubation period. The OAs include sorghum stubble and sugarcane bagasse that were low C quality (e.g., C:N:P ratio of 328:6.2:1 and 850:17.3:1, respectively) and less decomposed (e.g., low alkyl-C/o-alkyl-C ratio), and sugarcane mill mud that was high C quality (C:N:P ratio of 17:1.4:1) and more decomposed status. The results suggest that the quality of OAs is likely to control the dominant mechanisms of soil aggregation: (i) a quick top-down formation of aggregate hierarchy (~31 days) in the low C quality and less decomposed OAs; and (ii) a slow bottom-up formation of aggregate hierarchy (≥90 days) in the high C-quality and more decomposed OA. Over time, lowering the C-nutrient stoichiometric ratio of OAs (via exogenous nutrients) decreased aggregate stability by 30%, owing to accelerated breakdown/loss of OAs (i.e., by 16%). The exchangeable Ca²⁺ (from gypsum) was positively correlated to WMWD and water stable aggregates (>0.05 mm), which were not influenced by OAs or nutrients. In this dispersive clay subsoil, a long-term positive effect on soil aggregation occurred when improving either biochemical properties (e.g., microbial biomass and soil organic C) or chemical properties (e.g., soil dispersion, exchangeable sodium percentage, and pH), and an additive effect appeared when both properties were changed. This study provides critical information on the effects of OAs with variable C qualities, gypsum, and nutrients on structural stability with insights into strategies of sodic subsoil amelioration and soil C storage.

钠离子分散底土对干旱和半干旱地区的农业生产力和可持续性构成重大限制。石膏和有机改良剂 (OA) 已显示出改善土壤结构和肥力的潜力，并可能解决与这些分散土壤相关的限制。然而，OAs 的质量与土壤结构稳定性（即土壤团聚体）的动力学之间的机械联系，特别是在石膏和外源养分的相互作用影响下，仍然难以捉摸。我们量化了分散性粘土底土（δ ¹³ C -24.5‰）中不同骨料类别中的骨料稳定性（即湿平均重量直径，WMWD）和 OA-碳（C）的积累，无论是否施用 OA（ δ¹³ C -12.8 至 -14.3‰)、石膏和/或外源营养素（氮 (N) 和磷 (P)）在 270 天的潜伏期内。OA 包括低 C 质量（例如，C:N:P 比率分别为 328:6.2:1 和 850:17.3:1）和较少分解（例如、低烷基-C/o-烷基-C 比率），以及高 C 质量（C:N:P 比率为 17:1.4:1）和更多分解状态的甘蔗磨泥。结果表明，OAs 的质量可能控制土壤团聚的主要机制：（i）在低 C 质量和较少分解的 OAs 中快速自上而下形成团聚体等级（~31 天）；(ii) 在高 C 质量和更分解的 OA 中缓慢自下而上形成聚合层次结构（≥90 天）。随着时间的推移，由于 OA 加速分解/损失（即降低 16%），降低 OA 的 C 营养素化学计量比（通过外源性营养素）使聚集体稳定性降低了 30% 。可交换的 Ca ²⁺（来自石膏）与 WMWD 和水稳定聚集体（> 0.05 mm）呈正相关，不受 OA 或营养物质的影响。在这种分散的粘土底土中，当改善生化特性（例如微生物生物量和土壤有机碳）或化学特性（例如土壤分散性、可交换钠百分比和 pH 值）时，对土壤团聚产生长期的积极影响，并且当这两个属性都发生变化时，就会出现加性效应。本研究提供了关于具有可变碳质量、石膏和养分的 OA 对结构稳定性影响的关键信息，并深入了解了底土钠盐改良和土壤碳储存的策略。