Spatial sampling tools for representative soil sampling

Soil surveys provide information for farm environment plans, regional surveys, and national inventories. For large scale surveys of soil properties, field sampling is typically carried out on a selection of sites that are intended to be representative of the soil information on the landscape. There are many considerations involved in the decision where representative samples should be sited, dictated by the resource cost involved, site access restrictions, practical aspects of the soil sampling protocol, and the statistical efficiency of the samples that are gathered. While assessment of the “best” sample design for a survey can be undertaken by a statistician, it is often useful for the field scientist to understand how different sampling approaches affect the distribution of samples, and how compromises in sample designs affect the sampling result. Software packages for spatial sampling design have improved over recent years, but they can still be complicated for many who are not specialists in sampling design. This paper reports on the development of a graphical user interface (GUI) application tool to assist the field scientist understand some of the compromises involved in using different spatial sampling strategies. Using a shapefile of the study area as input, different spatial sampling strategies can be applied to select one or more versions of the required samples, and display them in the study area. Simple summary statistics are provided to provide some comparison between the methods. The completed design can be saved directly to an Excel spreadsheet with map coordinates for further analysis. In simple cases, the saved results can be used for direct use in the field. The intention is that the application can be used to improve understanding of the compromises involved in selecting sampling designs, and allows the field scientist more direct involvement in site selection, to allow sampling design options to be tested in terms of practical achievement and implications on statistical robustness. Introduction Soil surveys provide critical information for farm environment plans delineating soil patterns, as well as regional surveys, and national inventories detailing broad-scale soil properties. The analysis from these efforts typically requires a set of samples designed to be representative of the soil information on the landscape. In this sense, a representative sample can be defined as a group of points whose soil characteristics closely match the characteristics of the population of all soils in the study area. For example, if what is required is an estimate of some physical property (e.g. pH, carbon, Cd concentration) from soils in the high country grasslands, then the field study points should all be from high country grasslands, with characteristics that