Abstract

Soils play an important role in the balance of carbon on the global scale. The study of the carbon cycle in Calcareous soils has received less attention, while Calcareous soils cover a third of the world’s soils and most croplands of Iran. The aim of this study was to investigate soil organic carbon fractions and the relationship of soil organic carbon (SOC) with soil properties in 30 wheat farms of Calcisols of Alborz, Iran. To study the effects of soil geochemical properties, the data were subjected to cluster analysis to select samples with similar texture and low salinity. We applied a densimetric method using sodium iodide (NaI) to isolate light fraction (LF < 1.6 g/cm³), occluded fraction (OF < 1.8 g/cm³), and mineral-associated organic matter (MAOM > 1.8 g/cm³) of selected soils. Results showed that SOC decreased up to 61% throughout the soil profile. Mineral-associated organic matter had the highest proportion (more than 75%) of SOC in agricultural soils. The mean value of C/N reduced in mineral-associated organic matter compared to that of bulk soil, which indicates nitrogen concentration in this fraction. The study of soil properties suggested that calcium carbonate equivalent (CCE) could explain SOC content in calcareous soils, while extracted metals (iron, magnesium, and calcium) had a significant relationship with the organic carbon content of heavy fraction.

中文翻译：

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钙质耕作土壤中的土壤有机碳分数

摘要

土壤在全球范围内的碳平衡中发挥着重要作用。对钙质土壤碳循环的研究较少受到关注，而钙质土壤覆盖了世界三分之一的土壤和伊朗的大部分农田。本研究的目的是调查伊朗厄尔布尔士 Calcisols 的 30 个小麦农场的土壤有机碳组分以及土壤有机碳 (SOC) 与土壤性质的关系。为了研究土壤地球化学性质的影响，对数据进行聚类分析，选择质地相似、盐度较低的样品。我们应用使用碘化钠 (NaI) 的密度法来分离轻组分 (LF < 1.6 g/cm ³ )、吸留组分 (OF < 1.8 g/cm ³ ) 和矿物相关有机物 (MAOM > 1.8 g/cm 3 ) ³）选定的土壤。结果表明，整个土壤剖面的 SOC 下降了 61%。农业土壤中与矿物相关的有机质所占的 SOC 比例最高（超过 75%）。与大块土壤相比，矿物相关有机质中的 C/N 平均值降低，表明该部分中的氮浓度。土壤性质研究表明，碳酸钙当量（CCE）可以解释钙质土壤中的 SOC 含量，而提取的金属（铁、镁和钙）与重馏分的有机碳含量有显着关系。