Contents lists available at ScienceDirect Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag Original papers New perspectives to use Munsell color charts with electronic devices N.P. Kirillova a, ⁎ , J. Grauer-Gray b , A.E. Hartemink b , T.M. Sileova a , Z.S. Artemyeva c , E.K. Burova a a Soil Science Faculty, Moscow State University, Leninskie Gory, Moscow 119991, Russia b University of Wisconsin – Madison, Department of Soil Science, FD Hole Soils Lab, 1525 Observatory Drive, Madison, WI 53706, USA c V.V. Dokuchaev Soil Science Institute, Pyzhevskii 7, Bld. 2, Moscow 119017, Russia ARTICLE INFO Keywords: Soil color History of Munsell system Color measurement Flatbed scanners ABSTRACT This article considers the evolution of the use of the Munsell system for assessing soil color. In the 1920s, Munsell color disks were recommended for soil color measurement. Munsell soil color charts (MSCs) were introduced in the 1940s. In 1942, the American Standards Association recommended that spectrophotometers be used for quantitative measurements and the Munsell system be used only for the psychological characterization of color. Despite this recommendation, soil scientists have continued using MSCs to measure soil color semi-quantita- tively. The utility of MSCs for color determination depends on three qualities: ambiguity, adequacy and reliability. Quantitative color was measured with a spectrophotometer. Chip colors were compared using the CIELAB color difference (ΔE ab *). To examine ambiguity, we calculated the ΔE ab * for every possible MSC color chip pair. Considerable ambiguity was found; 60% of the chips had duplicates. Chips were considered duplicates if the color difference was barely perceptible visually (ΔE ab * < 3). To investigate adequacy, the color difference between 161 soil samples and their closest MSC chips was calculated. Only 52% of the samples had ΔE ab * < 3. This indicated that the color range of the MSC does not adequately cover the range of natural soil colors. To study the reliability of MSCs, an old and a new MSC were compared. The identically designated chips in the old and new MSC generally had color differences of less than 3. Only 16% had ΔE ab * > 3. In addition, chips within a chart or even within a sheet can fade over time in a non-uniform way. On the 2.5Y sheet, a stable group of color chips (∼63%) occurred. This stable group consisted of the chips that were the least prone to dis- coloration (ΔE ab * < 3). This study determined that the inadequacy and ambiguity of MSCs can be overcome by using MSCs in combination with flatbed scanners. MSCs can be used to calibrate flatbed scanners for the purpose of soil color measurement. A procedure is proposed. The procedure calibrates the scanner using 7 chips from the stable group of the 2.5Y sheet. This procedure enables the measurement of soil color inexpensively and efficiently. The high efficiency of the method was confirmed by testing the accuracy of the soil color determinations for 20 soil samples, covering a wide color range. The calibration procedure quadruples the precision of color estimation compared to solely using MSCs and results in soil color measurements close to those achievable with spectro- photometers. 1. Introduction Many diagnostic criteria and soil classifications are based on the color of horizons. For this purpose soil scientists often use the Munsell color system, identifying soil color by visually comparing albums of color chips with the color of the soil sample. The precursor to these albums, The Munsell Atlas of Color, was published over 100 years ago in 1915. These albums, commonly called Munsell color charts, have not changed significantly since the 1940s. Practically since the dawn of the U.S. Soil Survey, soil color has been a part of U.S. soil classification (Instructions to Field Parties, 1903; Simonson, 1993). Initially, soil color determination depended on in- dividual interpretation (Instructions to Field Parties, 1914). By the early 1920s, several soil scientists had recognized the need for soil color standards (Hutton, 1921; Hendrickson, 1922; Simonson, 1993). Early proposals for the development of soil color standards focused on standardizing the contemporary system of qualitative color de- scription, but the substitution of a numerical color system was soon https://doi.org/10.1016/j.compag.2018.10.028 Received 30 January 2018; Received in revised form 25 July 2018; Accepted 21 October 2018 ⁎ Corresponding author. E-mail address: npkirillova@soil.msu.ru (N.P. Kirillova). Computers and Electronics in Agriculture 155 (2018) 378–385 0168-1699/ © 2018 Published by Elsevier B.V. T