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Title: Measurement of soil color: a comparison between smartphone camera and the Munsell color charts

item Fan, Zhaosheng
item Herrick, Jeffrey - Jeff
item SALTZMAN, RICK - Non ARS Employee
item MATTEIS, C - University Of Colorado
item YUDINA, A - University Of Colorado
item NOCELLA, N - University Of Colorado
item CRAWFORD, E - University Of Colorado
item PARKER, R - University Of Colorado
item Van Zee, Justin

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2017
Publication Date: 9/7/2017
Citation: Fan, Z., Herrick, J.E., Saltzman, R., Matteis, C., Yudina, A., Nocella, N., Crawford, E., Parker, R., Van Zee, J.W. 2017. Measurement of soil color: a comparison between smartphone camera and the Munsell color. Soil Science Society of America Journal. 81:1139-1146.

Interpretive Summary: Soil color is an important indicator and attribute that can be used to characterize, classify, and differentiate soils, allowing it to be used alone or with other indicators to predict soil properties. The most common way to measure soil color is to use Munsell color charts (MCCs) that define soil color based on shade, lightness, and saturation. However, soil color observed using MCCs is strongly influenced by environmental conditions (e.g., illumination) as well as the knowledge, experience, and color vision (e.g., normal versus deficient) of observers, and thus still remains subjective, resulting in a lack of consistency among different observers. The goal of this study was to investigate the accuracy and precision of a new smartphone camera app to measure soil color under natural outdoor lighting conditions, and to compare the results with those based on ocular determinations with a MCC. Our results showed that using smartphone cameras to measure soil color under natural illumination in the field was as reliable as using MCCs, suggesting that smartphone and other mobile devices have the great potential to significantly enhance our ability to quickly and reliably measure soil color in the field.

Technical Abstract: Soil color is one of the most valuable soil properties for assessing and monitoring soil health. Here we present the results of tests of a new soil color app for mobile phones. The comparisons include various smartphones cameras under different natural illumination conditions (sunny and cloudy) and using Munsell color charts (MCCs). The measured soil color was then compared with the “true” soil color that was determined using a spectrophotometer to evaluate the performance of smartphone cameras (SPCs), compared to the MCCs. The results indicated that the soil color measured with the SPCs under both sunny and cloudy conditions was as good as that obtained using the MCCs. The accuracy of the measured soil color with SPCs was affected by the natural illumination conditions, with higher accuracy of soil color in the sun than where clouds were present. Additionally, our results also indicated that the uncertainty (variance) of the soil color measured with the SPCs in the sun was lower than that measured when the sun was obscured by clouds and with the MCCs. These results suggest that mobile-device cameras have the great potential to measure soil color outside in the field, with less subjectivity and uncertainty, compared to using MCCs.