面向数字土壤制图的土壤采样设计研究进展与展望

全球化土壤环境问题的出现对基础输入数据的精度、尺度和时序提出了更高要求,面向数字土壤制图的土壤采样研究得到了快速发展。首先利用文献计量学的方法定量化分析国内外土壤采样研究学科分布和研究热点变化;随后重点梳理了国内外土壤采样研究的文献,根据不同的土壤调查目的、调查区历史采样点将土壤采样设计分为:土壤全面采样设计、土壤补充采样设计、土壤验证采样设计和土壤监测采样设计;最后介绍了基于样点的推理制图方法。在此基础上,对未来在多尺度的土壤采样设计、土壤–环境因子关系的新型假设和采样设计中现实问题的量化等方面进行了展望,旨在为数字土壤调查工作的开展提供参考依据。

Review and Outlook of Designing of Soil Sampling for Digital Soil Mapping

The appearance of soil environmental problems, such as pollution and degradation, has stimulated researches on hydro-ecological simulation, soil resource management, soil carbon and nitrogen monitoring, etc., thus putting forward higher requirements on basic input data, like types and attributes of soils, in accuracy, scale and timing sequence and causing rapid development of the research on soil sampling oriented towards digital soil mapping. In this study, the bibliometric method was applied to quantitatively analyze variation of the researches at home and abroad in distribution of disciplines hotpot during the recent four decades since 1980. Based on collation and review of the literature, summarization was performed of methods widely used nowadays in soil sampling and speculative mapping, and discussions conducted about future trends of the research on sampling designing for digital soil mapping, in an attempt to provide a reference for development of digital soil survey. Results show: (1) Over the last four decades, hotspots of the research on soil sampling have been focused on theories, methods, techniques, means and strategies of soil sampling, soil management and utilization, digital soil mapping, etc., involving disciplines that have developed from a single field of soil science into a transdisciplinary research covering agronomy, engineering, soil science, environmental science and geography, etc., with theories, techniques and means turning from mere application of probability theory into combination of geostationary models, deep learning and knowledge mining, and focuses laid on application in ecological monitoring and protection, precision agriculture and polluted remediation. (2) Soil sampling designing is a process of selecting an appropriate sampling method to meet the specific goal of a soil survey based on certain prior knowledge. According to the purposes of a soil survey and soil sampling history of the surveyed area, soil sampling designs can be divided into four categories, i.e. comprehensive sampling, supplemental sampling, verification sampling and monitoring sampling. In regions lacking historical soil sampling data, comprehensive sampling can be implemented by appointing sampling sites randomly based on the designed sampling method to achieve uniform coverage of their geospatial space, or by laying out sampling sites with reference to environmental factors to realize coverage and optimization of feature spaces, while in regions rich in data. comprehensive sampling may better adopt model-based sampling methods. For supplemental sampling, sampling points should be laid out in locations low in similarity of environmental factors, or high in uncertainty of predictive mapping or both. For validation sampling, independent sampling points should be arranged in line with the sampling design for better validation effect. And monitoring sampling could be designed into spatial sampling and temporal sampling or both with sampling sites laid out based on the design and the model in combination. And (3) soil mapping is a process of realizing point-plane expansion with the aid of mathematical methods or spatial models based on soil-environment relationship and spatial autocorrelation of soil attributes. In soil mapping, cartographers should pay attention to adoption of environmental factors and efficiency of the method utilizing the information of variables of the sampling sites. Hereby, cartographers should choose a corresponding inference model to implement spatial expression of soil information. So studies in future should be oriented towards application and theory, like designing of multi-scale soil sampling, new hypothesis of soil-environment relationship hypothesis and quantification of realistic problems in soil sampling designing.