Estimation and implications of instrumental drift, random measurement error and nugget variance of soil attributes—a case study for soil pH

Abstract

SUMMARYWe propose a general model for soil pH measurement that includes instrumental drift, random measurement error, and random and correlated spatial variation. Methods for estimating these four components are described in detail. For soil pH in water, instrumental drift, random measurement error and random spatial variation (nugget effect) were greater than the corresponding quantities for soil pH in CaCl2. For both pH measurements, instrumental drift was quite marked. Measurement error and nugget effect were of a similar size. A modified kriging method is presented that takes into account the four‐component model proposed here. It is concluded that, for measuring soil chemical attributes, grid layouts should be supplemented by additional sites for the estimation of short‐range variation, that laboratory sampling designs should include controls, and that field measurements should be adjusted for instrumental drift prior to being used for spatial contouring or kriging.