Pedosphere 27(2): 344--357, 2017
ISSN 1002-0160/CN 32-1315/P
©2017 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Regional soil mapping using multi-grade representative sampling and a fuzzy membership-based mapping approach
YANG Lin1,2, A-Xing ZHU2,3,4,5,6, ZHAO Yuguo1, LI Decheng1, ZHANG Ganlin1, ZHANG Shujie7,Lawrence E. BAND8
1State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China)
2 State Key Laboratory of Resources and Environment Information System, Institute of Geographical Sciences and Resources Research, Chinese Academy of Sciences, Beijing 100101 (China)
3 Key Laboratory of Virtual Geographic Environment (Nanjing Normal University), Ministry of Education, Nanjing 210023 (China)
4 Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, School of Geo- graphy, Nanjing Normal University, Nanjing 210023 (China)
5 State Key Laboratory Cultivation Base of Geographical Environment Evolution (Jiangsu Province), Nanjing 210023 (China)
6 Department of Geography, University of Wisconsin-Madison, Madison WI 53706 (USA)
7 China Academy of Urban Planning & Design, Beijing 100037 (China)
8 Institute for the Environment, University of North Carolina, Chapel Hill, Chapel Hill NC 27599 (USA)
      High-resolution and detailed regional soil spatial distribution information is increasingly needed for ecological modeling and land resource management.For areas with no point data, regional soil mapping includes two steps: soil sampling and soil mapping.Because sampling over a large area is costly, efficient sampling strategies are required.A multi-grade representative sampling strategy, which designs a small number of representative samples with different representative grades to depict soil spatial variations at different scales, could be a potentially efficient sampling strategy for regional soil mapping. Additionally, a suitable soil mapping approach is needed to map regional soil variations based on a small number of samples. In this study, the multi-grade representative sampling strategy was applied and a fuzzy membership-weighted soil mapping approach was developed to map soil sand percentage and soil organic carbon (SOC) at 0--20 and 20--40 cm depths in a study area of 5900 km2 in Anhui Province of China.First, geographical sub-areas were delineated using a parent lithology data layer.Next, fuzzy c-means clustering was applied to two climate and four terrain variables in each stratum. The clustering results (environmental cluster chains) were used to locate representative samples. Evaluations based on an independent validation sample set showed that the addition of samples with lower representativeness generally led to a decrease of root mean square error (RMSE).The declining rates of RMSE with the addition of samples slowed down for 20--40 cm depth, but fluctuated for 0--20 cm depth.The predicted SOC maps based on the representative samples exhibited higher accuracy, especially for soil depth 20--40 cm, as compared to those based on legacy soil data.Multi-grade representative sampling could be an effective sampling strategy at a regional scale.This sampling strategy, combined with the fuzzy membership-based mapping approach, could be an optional effective framework for regional soil property mapping. A more detailed and accurate soil parent material map and the addition of environmental variables representing human activities would improve mapping accuracy.
Key Words:  fuzzy clustering, parent lithology, representative grade, sampling strategy, soil spatial variations
Citation: Yang, L., Xing, Z., Zhao, Y., Li, D., Zhang, G., Zhang, S. and Band, E. 2017. Regional soil mapping using multi-grade representative sampling and a fuzzy membership-based mapping approach. Pedosphere. 27(2): 344-357.
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