Characteristics of soil exchangeable potassium according to soil color and landscape in Ferralsols environment

Abstract The use of soil color as Munsell data was explored for in situ indication of soil potassium (K) availability toward a friendly method of agricultural land survey. Soil contents of K, calcium, and magnesium were determined for 998 upland soil samples from Côte d’Ivoire (7–10°N). Soil depths (0–20, 20–60, 60–80, and 80–150 cm), redness ratio (RR), and redness factor (RF) were considered. Significant association was observed between K-levels (high, medium, and low) in topsoil and its color hue, and the highest cumulative frequency of 2.5YR in high and medium levels was characterizing the hill slope position (summit and upper slope). Deep horizon, foot slope, and yellowish color (7.5YR and 10YR) were more relevant to low K-level. Significant linear regressions of soil content of K were observed according to both redness indices indifferently to the topographic positions and soil depths in some extend. Of these finding in the line of folk knowledge, RR and RF are recommended for in situ measurement of soil K, and 2.5YR as color hue may be use as indicator of K-enriched soil at hill slope position.