Abstract. In the natural environment, soils undergo wetting and drying (WD) cycles due to precipitation and evapotranspiration. The WD cycles have a profound impact on soil physical, chemical, and biological properties and drive the development of structure in soils. Degraded soils are often lacking structure and the effect of organic amendments and WD cycles on structure formation of these soils is poorly understood. The aim of this study was to evaluate the role of biotic and abiotic factors on aggregate formation and stabilisation of sodic soils after the addition of gypsum and organic amendments (feedlot manure, chicken manure, lucerne pallets, and anionic poly acrylamide). Amended soils were incubated at 25 °C over four WD cycles, with assessment of soil microbial respiration, electrical conductivity, pH, sodium adsorption ratio (SAR), aggregate stability in water (ASWAT), aggregate size distribution, and mean weight diameter. Our results demonstrate that WD cycles can improve aggregate stability after the addition of amendments in sodic Vertisols, but this process depends on the type of organic amendment. Lucerne pellets resulted in highest soil microbial respiration, proportions of large macroaggregates, and mean weight diameter. In contrast, dispersion was significantly reduced when soils were treated with chicken manure, whilst PAM only had a transient effect on aggregate stability. When these organic amendments were applied together with gypsum, the stability of aggregates was further enhanced, and dispersion became negligible after the second WD cycle. The formation and stability of small macroaggregates was less dependent on the type of organic amendments and more dependent on WD cycles as the proportion of small macroaggregates also increased in control soils after four WD cycles, highlighting the role of WD cycles as one of the key factors that improves aggregation and stability of sodic Vertisols.

中文翻译：

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干湿循环、有机质和石膏在钠质 Vertisols 的结构形成和稳定性中起关键作用

摘要。在自然环境中，由于降水和蒸散，土壤会经历干湿 (WD) 循环。WD 循环对土壤的物理、化学和生物特性产生深远的影响，并推动土壤结构的发展。退化的土壤通常缺乏结构，有机改良剂和 WD 循环对这些土壤结构形成的影响知之甚少。本研究的目的是评估在添加石膏和有机改良剂（饲养场粪肥、鸡粪、苜蓿托盘和阴离子聚丙烯酰胺）后，生物和非生物因素对钠质土壤团聚体形成和稳定的作用。改良后的土壤在 25°C 下孵育四个 WD 循环，评估土壤微生物呼吸、电导率、pH、钠吸附比 (SAR)、骨料在水中的稳定性 (ASWAT)、骨料粒度分布和平均重量直径。我们的研究结果表明，WD 循环可以提高在钠化 Vertisol 中添加改性剂后的聚集体稳定性，但这一过程取决于有机改性剂的类型。Lucerne 颗粒导致最高的土壤微生物呼吸、大团聚体的比例和平均重量直径。相比之下，当土壤用鸡粪处理时，分散显着降低，而 PAM 仅对骨料稳定性有短暂的影响。当这些有机改良剂与石膏一起使用时，骨料的稳定性进一步增强，并且在第二次 WD 循环后分散变得可以忽略不计。