Simple measures of appropriate levels of soil organic matter are needed for soil evaluation, management and monitoring, based on readily measurable soil properties. We test an index of soil organic matter based on the soil organic carbon (SOC) to clay ratio, defined by thresholds of SOC/clay ratio for specified levels of soil structural quality. The thresholds were originally delineated for a small number of Swiss soils. We assess the index using data from the initial sampling (1978–83) of the National Soil Inventory of England and Wales, covering 3,809 sites under arable land, grassland and woodland. Land use, soil type, annual precipitation and soil pH together explained 21% of the variance in SOC/clay ratio in the dataset, with land use the most important variable. Thresholds of SOC/clay ratio of 1/8, 1/10 and 1/13 indicated the boundaries between “very good”, “good”, “moderate” and “degraded” levels of structural condition. On this scale, 38.2, 6.6 and 5.6% of arable, grassland and woodland sites, respectively, were degraded. The index gives a method to assess and monitor soil organic matter at national, regional or sub-regional scales based on two routinely measured soil properties. Given the wide range of soils and land uses across England and Wales in the dataset used to test the index, we suggest it should apply to other European soils in similar climate zones.

中文翻译：

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什么是良好的土壤有机质水平？基于有机碳与粘土比率的指标

土壤评价、管理和监测需要基于易于测量的土壤特性，对适当水平的土壤有机质进行简单的测量。我们测试了基于土壤有机碳 (SOC) 与粘土比率的土壤有机质指数，该比率由特定土壤结构质量水平的 SOC/粘土比率阈值定义。阈值最初是为少数瑞士土壤划定的。我们使用英格兰和威尔士国家土壤清单的初始抽样（1978-83 年）的数据评估该指数，涵盖耕地、草地和林地下的 3,809 个地点。土地利用、土壤类型、年降水量和土壤 pH 值共同解释了数据集中 SOC/粘土比率变化的 21%，其中土地利用是最重要的变量。SOC/粘土比例的阈值为1/8，1/10 和 1/13 表示结构状况的“非常好”、“良好”、“中等”和“退化”水平之间的界限。在这个规模上，分别有 38.2%、6.6% 和 5.6% 的耕地、草地和林地退化。该指数提供了一种基于两种常规测量的土壤特性在国家、区域或次区域尺度上评估和监测土壤有机质的方法。鉴于用于测试该指数的数据集中英格兰和威尔士的土壤和土地用途范围广泛，我们建议它应该适用于类似气候区的其他欧洲土壤。基于两个常规测量的土壤特性的区域或次区域尺度。鉴于用于测试该指数的数据集中英格兰和威尔士的土壤和土地用途范围广泛，我们建议它应该适用于类似气候区的其他欧洲土壤。基于两个常规测量的土壤特性的区域或次区域尺度。鉴于用于测试该指数的数据集中英格兰和威尔士的土壤和土地用途范围广泛，我们建议它应该适用于类似气候区的其他欧洲土壤。