Accuracy and accessibility in soil color determination: A comparative analysis of Munsell Chart, colorimeter, and smartphone in Amazonian soils

Abstract

Soil color is a key diagnostic property and fundamental morphological characteristic that provides valuable insights into its properties and pedological processes, and is widely used in the taxonomic classification of soils. However, traditional methods of soil color determination, such as the Munsell color chart, are limited by the subjectivity of visual interpretation, which can lead to significant variations in results. This study aimed to compare the accuracy of soil RGB (Red, Green, Blue) color parameters obtained by three distinct methods: Munsell color chart, colorimeter, and smartphone, with a focus on minimizing subjectivity and improving measurement reliability in Amazonian soils. We analyzed 98 samples from Capanema, Pará (Brazil), collected from two layers (0.00–0.20 m and 0.20–0.40 m) under both dry and moist conditions. Data were processed using Spearman correlation, ANOVA, and Lin’s concordance correlation coefficient. Results showed that the Munsell color chart exhibited the highest variability and poorest agreement, particularly in moist conditions and deeper layers. The colorimeter and smartphone showed superior consistency, with smartphone imaging proving to be a viable, low-cost field alternative. Digital soil color analysis via smartphones significantly reduced measurement subjectivity and uncertainty. Results demonstrate that smartphone-based color analysis offers a reliable method for Amazonian soils, effectively converting common devices into precise scientific tools for agricultural and environmental management. This mobile approach enables standardized field measurements in resource-limited settings, representing an innovative advancement for soil characterization and digital tools, particularly in Amazon biome.