ABSTRACT

Identifying the soil properties that control soil organic carbon (SOC) storage is a critical step to monitor and manage SOC at regional and global scales. While clay content has been commonly used to explain SOC variation and to model SOC dynamics, recent studies point to the significant control of extractable metal phases such as pyrophosphate extractable Al (Al_p) for a range of soil types. Phosphate adsorption coefficient (PAC), soil’s capacity to adsorb phosphate, is known to show strong positive correlation with Al_p. The soil database maintained by the national farmland fixed–point survey contains basic soil attributes including SOC and PAC and covers approximately 20,000 sites that belong to Andosols and Lowland soil great groups, representing roughly 70% of the arable land in Japan (MAT range from 5.3 to 22.3 °C). Using the database, we found that PAC showed more significant positive correlation with SOC compared to clay and silt–clay contents for both Lowland soils and Andosols. The OC:Al_p ratio was estimated from the slope of SOC:PAC regression line for all soil groups and great groups ranged from 3.35 to 10.5 (mol:mol), which was within the range shown in previous studies on volcanic and spodic soils. The ANCOVA test further revealed that the SOC–PAC relationship was significantly affected by soil temperature regime in both soil group and soil great group levels (both p < 0.0001). All four soil groups within Lowland soils showed a similar temperature-dependent trend in the SOC:PAC ratio with little variation among the groups. The soil groups within Andosols, however, had no clear temperature trend, suggesting the influence of other factors that remain to be elucidated in future. We concluded that PAC was the more effective indicator of SOC than clay content for the major arable soils in Japan and that the PAC–SOC relationship was partly controlled by soil temperature and soil group. Further study to assess the role of Al_p and the contribution of other factors such as land use and management type is important as major portions of the SOC variation was not explained by PAC.

摘要

确定控制土壤有机碳 (SOC) 储存的土壤特性是在区域和全球范围内监测和管理 SOC 的关键步骤。虽然粘土含量通常用于解释 SOC 变化和模拟 SOC 动力学，但最近的研究表明，对一系列土壤类型的可提取金属相如焦磷酸盐可提取铝 (Al _p )的显着控制。磷酸盐吸附系数 (PAC)，即土壤吸附磷酸盐的能力，与 Al _p显示出强烈的正相关关系. 由国家农田定点调查维护的土壤数据库包含包括 SOC 和 PAC 在内的基本土壤属性，涵盖了属于 Andosols 和 Lowland 土壤大类群的约 20,000 个站点，约占日本耕地的 70%（MAT 范围从 5.3到 22.3 °C）。使用该数据库，我们发现与低地土壤和安多溶胶的粘土和粉砂-粘土含量相比，PAC 与 SOC 显示出更显着的正相关。OC:Al _p比率是根据所有土壤组和大组的 SOC:PAC 回归线的斜率估计的，范围为 3.35 到 10.5 (mol:mol)，这在之前对火山和火山土壤的研究中显示的范围内。ANCOVA 检验进一步表明，土壤组和土壤大组水平的土壤温度状况显着影响 SOC-PAC 关系（均p< 0.0001)。低地土壤中的所有四个土壤组的 SOC:PAC 比率都显示出类似的温度依赖性趋势，组间变化很小。然而，安多索内的土壤群没有明显的温度趋势，表明其他因素的影响有待未来阐明。我们得出结论，PAC 是日本主要耕地土壤 SOC 比粘土含量更有效的指标，并且 PAC-SOC 关系部分受土壤温度和土壤组的控制。进一步研究评估 Al _p的作用以及其他因素（如土地利用和管理类型）的贡献很重要，因为 PAC 未解释 SOC 变化的主要部分。