Soil water content and photosynthetically active radiation influences soil color assessment

Abstract

Determining Munsell soil color in the field is subject to environmental conditions, including soil water content (SWC) and light intensity. New digital spectral technology designed for determining soil color may offer accurate assessments regardless of environmental conditions. This study was conducted to determine the impacts of SWC and light on visual observations and digital measurements of soil color value and chroma, the two color components most important for soil use interpretations for siting and designing onsite wastewater systems. Munsell color was measured using the XRite Capsure™ and visually using Munsell Color Books on 111 soil horizons from three South Carolina regions. While, in general, higher color values and lower chromas were determined from oven dried peds in comparison to field moist peds, the influence of SWC was region specific. Of most importance were higher color chromas documented from field moist peds compared to oven dried peds in the Coastal region. In this region, gley chromas were determined in unsaturated soils emphasizing the importance of carefully evaluating other landscape features when interpreting the soil for onsite wastewater treatment. While SWC affected the agreement between digital measurements and visual observations, in most regions the difference was less than one color chip and of no practical significance. Varying photosynthetically active radiation (PAR) did not affect digital measurements and had minimal influence on visual observations. Digital measurements of soil color value and chroma may offer validation of soil color under varying lighting conditions and could be a promising tool for training new soil evaluators in color assessment.