The roles of sampling depth, lateral profile density and vertical sampling density in 3D digital soil mapping of soil organic carbon
Mei-Wei Zhang,
Xiao-Lin Sun,
Xiao-Qing Wang,
Hua-Lei Yang,
Hui-Li Wang,
Zhi-Gang Huang,
Dai-Hua Jiang,
Yun-Jin Wu
Affiliations
Mei-Wei Zhang
Carbon-Water Research Station in Karst Regions of Northern Guangdong, School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China
Xiao-Lin Sun
Carbon-Water Research Station in Karst Regions of Northern Guangdong, School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China; Guangxi Key Laboratory of Agro-Environment and Agro-Product Safety, College of Agriculture, Guangxi University, 530004 Nanning, China; Corresponding authors at: Rm. 302, Building 572, Sun Yat-sen University, 135 Xingang West Road, Guangzhou 510275, China (X.-L. Sun). Nanjing Institute of Environment Sciences, Ministry of Environment Protection, 8 Jiangwangmiao Street, Nanjing 210042, China (Y.-J. Wu).
Xiao-Qing Wang
Carbon-Water Research Station in Karst Regions of Northern Guangdong, School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China
Hua-Lei Yang
Carbon-Water Research Station in Karst Regions of Northern Guangdong, School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China
Hui-Li Wang
Guangxi Forestry Research Institute, Nanning 530002, China
Zhi-Gang Huang
Guangxi Key Laboratory of Agro-Environment and Agro-Product Safety, College of Agriculture, Guangxi University, 530004 Nanning, China
Dai-Hua Jiang
Guangxi Key Laboratory of Agro-Environment and Agro-Product Safety, College of Agriculture, Guangxi University, 530004 Nanning, China
Yun-Jin Wu
Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of the People's Republic of China, Nanjing 210042, China; Corresponding authors at: Rm. 302, Building 572, Sun Yat-sen University, 135 Xingang West Road, Guangzhou 510275, China (X.-L. Sun). Nanjing Institute of Environment Sciences, Ministry of Environment Protection, 8 Jiangwangmiao Street, Nanjing 210042, China (Y.-J. Wu).
Sampling density and depth play crucial roles in three-dimensional (3D) soil modeling and prediction, particularly in digital soil mapping (DSM). However, previous studies have yielded inconsistent and even contradictory results regarding impacts of sampling density and depth on the accuracy of 3D DSM. Hence, this study aimed to evaluate the impacts of sampling depth, vertical sampling density and lateral profile density on 3D soil mapping accuracy based on a case study of soil organic carbon (SOC). To achieve this, a comprehensive analysis was conducted based on 511 soil samples collected from 111 profiles in a local hilly area spanning 5.52 km2 in China. A 3D regression geostatistical approach was employed for the analysis. The results revealed that samples taken from different depth intervals exhibited varying degrees of importance in relation to prediction accuracy. Notably, a reduced number of surface soil samples (0–0.3 m) led to significant fluctuations in the accuracy of predictions for the entire soil profile. Furthermore, a lower number of subsurface soil samples (0.3–0.6 m) also diminished the overall prediction accuracy, while the influence of deeper soil samples (0.6–1.2 m) on the overall accuracy was relatively less pronounced. Reducing the number of profiles for calibration led to significantly worse and more variable prediction accuracy, compared to reducing vertical samples. For 3D mapping, this study recommends prioritizing the collection of additional lateral profiles, specifically focusing on surface and subsurface soils, especially for properties that display vertical variation similar to SOC.
