DRIFT Spectroscopy to Assess Cover Crop and Corn Stover Decomposition in Lab-Incubated Soil

Abstract

Cover crops are recommended for improving soil quality; however, the assessment of their benefits to soil is difficult and has typically involved the use of tedious, destructive methods. This study evaluated the applicability of diffuse reflectance infrared fourier transform (DRIFT) spectroscopy, a rapid nondestructive method for its potential to characterize soil organic constituents and plant residue decomposition processes. Soil from a 4-yr autumn cover cropping trial with a no cover crop control was amended with crop residues and used in a 72-d incubation study where data from DRIFT spectroscopy were compared with evolved CO₂ in measuring decomposition of cover crop biomass with (+S) and without (-S) corn stover residue. Treatment differences within model parameters of polysaccharide-C (1170–950 cm⁻¹ spectral region) decomposition curves were similar to those generated from the C decay curves. All soil amendment treatments had lower C mineralization and polysaccharide decomposition rates compared with the control, which suggests that the cover crops tested have the potential in the short-term to replenish labile organic C pools and to reduce C losses compared with the no cover crop control. In soil amended with crop residues DRIFT spectra revealed a disappearance of bands corresponding to labile polysaccharide-C during the incubation, which related to CO₂ evolution and was consistent with labile aliphatic-C bands (2930 cm⁻¹). This is the first study to demonstrate the use of DRIFT spectroscopy to assess crop residue decomposition in a soil matrix.