Determining the relative importance of climate and soil properties affecting the scores of visual soil quality indicators with dominance analysis

In this study, we have analyzed the relationships of four manageable soil properties, soil texture, and climate variables on the scores of visual indicators of 132 soils across Europe and China. Correlations differed in acid-to-neutral and alkaline soils, both in strength and direction, which gave rise to the different rankings of the importances of the explanatory variables for each visual indicator. In alkaline soils, higher soil pH values significantly affected the score of the visual indicators and dominated other variables for most visual indicators; in acid soils, only the "presence of a tillage pan" was affected by pH, and, for most visual indicators, soil organic matter (SOM) and labile organic carbon (LOC) dominated other manageable variables. In both soil reaction groups, climate variables covaried similarly in terms of direction but with different significances for different indicators; the dominance of the variables was dependent on soil reaction. Eight out of 16 visual indicators (eight per reaction group) had a statistically significant dominant explanatory variable (soil property or climate variable). The soil pH must be accounted for when interpreting visual indicators of soils with more extreme pH (both acid and alkaline).