Pedogenic variables with color indices of rubified Alfisols in the Kakalachinte microwatershed, Karnataka, South India

Abstract

Soil properties and processes can often be estimated by soil color, which provides valuable information about composition and other properties. We focused on the morphology, particle size distribution, and chemical properties of Alfisols in Kakalachinte microwatershed, Karnataka, India. Soil redness indices were calculated: Buntley's and Westin's rate (BWR), Hurst's rate (HR); Torrent’ rates (TR1 and TR2); Barrón's and Torrent's rates (BTR1 and BTR2), and Viscarra's rate (VR). The Munsell notation was converted to the CIE (Commission Internationale del'Eclairage, CIE) Lab system, Lab model: L*, luminance, a*, redness, and b*, yellowness of moist soil samples. Forty-five soil samples were characterized for texture, soil reaction (pH), electrical conductivity, calcium carbonate content, organic carbon (OC) content, exchangeable cations (sodium, Na; potassium, K; magnesium, Mg; and calcium, Ca), base saturation (BS), and cation exchange capacity (CEC). The pH of the soils ranged from strongly acid (pH of 5.25) to strongly alkaline (pH of 8.73). These soils exhibited low CEC, with a mean of 8.36 cmol(+)/kg and a coefficient of variation of >35%. The BS was found to be >70%, with a dominance of exchangeable Ca (6.93 ± 1.08 cmol(+)/kg). Correlation analysis revealed strong positive relationships between OC and the L* value (r = 0.6**). The correlation results revealed a strong positive correlation of a* value with TR1 (r = 0.54**), significant negative relationship between L* and BTR1 (r = −0.54*), BTR2 (r = −0.525*), and VR (r = −0.53*). Regression between soil OC and the L* value showed R² of 0.40 and RMSE of 0.01; soil exchangeable K and Mg with the R² = 0.74; RMSE = 0.12 and the R² = 0.42; RMSE = 0.11 at p < 0.001. The study highlights the importance of converting Munsell color notation to the CIELab system for understanding the rubification process in relation to soil properties in Alfisols at the microwatershed level.