Cross-reference for relating Genetic Soil Classification of China with WRB at different scales

Soil classification systems are not consistent between countries or organizations thereby hindering the communication and organizational functions they are intended to promote. World Reference Base for soil resources (WRB) was endorsed and adopted by the International Union of Soil Sciences (IUSS) as the standard for soil correlation and international communication. As a widely used classification system in China, Genetic Soil Classification of China (GSCC) differs from WRB in its underlying understanding about the genetic process. The differences limit communication between Chinese and international soil scientists because there is no standard cross-reference between GSCC and WRB. This paper describes a cross-reference of GSCC to WRB at different scales. The basic soil data set used in the study includes 7292 soil profile data (representative of soil series) collected throughout China. First, a brief history of soil classification in China is provided to familiarize readers with GSCC and its origins. Second, cross-reference at the pedon scale is addressed based on data compiled from 51 monoliths acquired in China by the International Soil Reference and Information Centre (ISRIC) in the 1980s and 1990s. Each of GSCC's 7292 soil series is classified into their equivalent reference soil groups according to the WRB soil reference key. Pedon scale cross referencing is discussed using the database from the Second National Soil Survey of China. Third, the concept and calculation of referencibility is introduced and the process for cross-referencing soil classification systems at national scale is addressed. GIS based analysis generates 60 reference results between GSCC soil great groups and WRB reference group. Results demonstrate that there is great variability in the maximum referencibility between soil great groups of GSCC and WRB soil groups, which ranged from 29.4% to 100%. In terms of the maximum referencibility, it can be divided into three categories: high (80%–100%), intermediate (50%–80%), and low (< 50%). Among the 60 soil great groups of GSCC, 12 could be labeled as high maximum referencibility, 27 categorized as medium maximum referencibility and the remaining 21 are associated with low maximum referencibility. Finally, the main cause of low maximum referencibility is explored and the potential solution to improve cross reference accuracy was proposed.