Description and spatial inference of soil drainage using matrix soil colours in the Lower Hunter Valley, New South Wales, Australia

Analysis of soil color variables and their relationships between two field-based methods and its potential application for wetland soils

While the Munsell Soil Color Chart (MSCC) is the most frequently used, well-established field method for reading soil color, the Nix Color Sensor (NCS) is an inexpensive, app-based alternative that can complement or potentially substitute for the MSCC. Soils were collected and their colors were measured from four forested sites across Northern Virginia within the Chesapeake Bay Watershed using both the MSCC and NCS. Three MSCC variables and 15 NCS variables were collected in the field; a methodology was established to use these "measured" (M) variables to derive 9 NCS calculated (C) variables. A stepwise correlation identified NCS variables most suitable for relating the NCS to each of the MSCC attributes: hue (H), value (V), and chroma (C_M). Ultimately, H, V, and C_M were deemed to be best represented by H_RGB calculated from the RGB color space (ρ = 0.56)_, L from the CIE-Lab color space (ρ = 0.73), and ẑ = Z/(X + Y + Z) from the XYZ color space (ρ = -0.80), respectively (p < 0.001). The corresponding explanatory powers of final NCS variables (i.e., H_RGB, L, and ẑ) for H, V, and C_M were 26%, 54%, and 62%, respectively (p <0.01). Significant differences in ẑ between soils identified as hydric and nonhydric, but lack of nonoverlapping ranges, indicate a potential for the NCS to complement the MSCC in assessing wetland soil color in an accessible and reproducible manner, including hydric soil identifications for wetland delineation practices. Further study with more data over various types of soils is necessary to establish stronger relationships between the NCS and MSCC. Nonetheless, the method of characterizing soil color variables from the two field methods presented in the study can serve as a template for future studies or environmental education programs desiring to use the NCS as a complement to the MSCC.