一种基于样点代表性等级的土壤采样设计方法

采样设计是获取土壤空间分布信息的关键环节,直接影响到土壤制图的精度。目前常用的采样设计方法大多存在着设计样本量大、采样效率不高的问题。当可投入资源难以完成一次性大量采样时,采样往往需要多次、分批进行。然而现有分批采样方法多考虑各批采样点在地理空间的互补性,可能造成样本点在属性空间的重叠,影响采样资源的高效利用。鉴于此,本研究通过对与土壤在空间分布具有协同变化的环境因子进行聚类分析,寻找可代表土壤性状空间分布的不同等级类型的代表性样点,建立一套基于代表性等级的采样设计方法。将该采样方法应用于位于黑龙江省嫩江县鹤山农场的研究区,利用所采集的不同代表性等级的样点进行数字土壤制图并进行验证,探讨采样方案与数字土壤制图精度的关系,以评价本文所提出的采样方法。结果表明,通过代表性等级最高的少量样点可获取研究区的大部分主要土壤类型(中国土壤系统分类的亚类级别),且制图精度较高;随着代表性等级较低样点的加入,土壤图精度提高;但当样点增加到一定数量时,土壤图的精度变化不大。因此,与样点数相比,样点的代表性高低对制图精度的影响更大。该方法所提出的代表性等级可以为样点采集顺序提供参考,有助于设计高效的逐步采样方案。

A soil sampling method based on representativeness grade of sampling points

Sampling design plays a critical role in capturing information about spatial distribution of soils, influences directly the accuracy of samples-based soil mapping. The commonly used methods are often confronted with such problems as the need for large amounts of samples and low sampling efficiency. When the resources available are inadequate for accomplishing a large volume of sampling once for all, additional sampling has to be done many times and in batches. However, the present in-batches sampling methods mostly take into account supplementality of the batches of sampling points in geographic space, which lead to overlapping of the sampling points in attribute space, affecting efficient utilization of the resources. In view of this, clustering analysis of soil environmental co-variates was performed to explore for sampling points representative of different grades of soil spatial distribution and to formulate a sampling designing method based on representativeness grade. This proposed method was applied to the study area located in Heshan Farm, Nenjiang County, Heilongjiang Province, and digital soil mapping was done using selected sampling points of different representativeness grades for verification of the methods. Results show that only a small number of sampling points of the highest grade could obtain most of the main soil types (sub-order in Chinese Soil Taxonomy) and soil mapping was high in accuracy; and addition of sampling points lower in representative grade could raise the accuracy of soil mapping; but the accuracy did not improve much when the number of sampling points added exceeded a certain level. Therefore, compared with the number of sampling points, representativeness grade of the points was more important to accuracy of soil mapping. The representativeness grade system proposed in this paper can be used as reference for sequencing of sampling points and is contributive to formulation of high-efficiency stepwise sampling design.