DEVELOPMENT OF AN ON-THE-GO SOIL PH MAPPING METHOD: ANALYSIS OF MEASUREMENT VARIABILITY

Abstract

An automated system for mapping soil pH on-the-go has been developed, tested, and commercialized. This systemis capable of determining soil pH approximately every 10 s as it moves across a field. When georeferenced, thesemeasurements could be used to construct soil pH maps that can be involved in farm management decision process. This methodfor on-the-go soil pH mapping uses flat surface ion-selective electrodes to directly measure the pH of moist soil. The prototypesystem was evaluated in a field with artificially created areas corresponding to acidic and neutral soil conditions. Testsrevealed that the resulting standard error (measurement error superimposed on the effects of soil micro variability) was foundto be 0.38 pH. The standard laboratory procedure (measurement of soil pH in 1:1 weight-to-weight soil-water solution)performed on the same set of samples resulted in 0.24 pH standard error. In addition, various laboratory experiments showedhigh correlation between soil pH measured directly on naturally moist samples and soil solutions (R2 = 0.93 - 0.96). Fieldevaluation of automated soil pH mapping indicated that automated sampling did not introduce a significant source of errorand produced the same variance of measurements within relatively homogeneous field areas as measurements performeddirectly on manually extracted soil samples.