COMPARATIVE STUDY OF THE MID-IR SPECTROSCOPY AND CHEMICAL METHOD FOR SOIL PHYSICAL AND CHEMICAL PROPERTIES

Abstract

Mid-IR spectroscopy is a fast soil analytical tool and can serve as alternative to the time consuming and hazardous chemical methods for the determination of soil physical and chemical analyses. To determine the degree of correlation between these two methods, 110 soil samples from the derived savanna region of Nigeria were analyzed using both chemical and spectroscopic methods. The MIR absorbance spectra were recorded in the range of 4000 to 400 cm-1 (2500-25000 nm) with 110 scans. Before the absorbance spectra were calibrated to predict soil properties, principal component analysis was conducted to detect sample outliers (6 out of 110 scans were identified as outliers) in the raw data set of the spectra and excluded. Satisfactory predictions (r2 = 0.65 - 0.75) were obtained for sand, silt and clay as regards the physical properties as well as total C, total N, P, Ca, Mg, K, Mn, Fe, Cu ( all determined using mehlich-3 extractant) for soil chemical properties. However, poorer predictions (r2 = 0.61-0.64) were obtained for mehlich 3-Na and Zn only.  With this high degree of prediction, it can be concluded that mid-IR spectroscopy has the potential to provide rapid and cost effective estimates of some soil physical and chemical properties.