Handheld‐Colorimeter‐Based Soil Color Survey of Red Soils in SW Brandenburg, North German Lowlands

ABSTRACT

Handheld colorimeters are a relatively novel tool in soil science that allow the objective measurement of soil color, potentially even in situ. Here we set out to assess the measurement reproducibility of two low‐cost colorimeters under simulated field conditions. We study the spatial distribution of a distinctly red soil in southwestern Brandenburg, Germany by means of a color survey on near‐surface soil samples. These soils in general can be classified as Rhodic Arenosols (Chromic/Rhodic) and are characterized by increased concentrations of total iron and the reddening iron oxides hematite and presumably maghemite. The process of a regionally uncharacteristic iron oxide dynamic was termed para‐rubefication in the past and its exact workings under real pedogenic conditions are subject to discussion and ongoing research. We show that using the Nix Pro 2 and Nix Mini 3 colorimeters results in almost equally reliable color measurements on ungrounded, moist soil samples with direct device‐soil contact. Using colorimeters enables the direct application of other color notation systems like CIELab, without converting Munsell colors. This is shown to be beneficial when detecting redness in soils via a modified qualitative soil redness index, as the comparably broad Munsell hue chips can potentially obscure fainter traces of redness in soils. Our soil redness survey shows that para‐rubefication appears to be a heavily localized process on shoulder‐ and backslope positions that becomes active within several meters horizontally and several decimeters vertically. This study promotes the use of novel sensor technology in soil science and gives a first high resolution mapping of the para‐rubefication process, facilitating further research into the complex iron‐oxide dynamics and spatial distribution of affected soils.