Biological Stability of Carbon and Nitrogen in Organic Products and Crop Residues using Fourier-Transform Near-Infrared Reflectance Spectroscopy

Lignin plus cutin (LIC) content and biological stability index (BSI) are well-recognized indexes of potentially recalcitrant carbon (C) in organic products, and C / nitrogen (N) and lignin/N ratios have been related to potentially mineralizable N (PMN). Our objective was to use Fourier-transform near-infrared (FT-NIR) spectroscopy to estimate PMN and BSI of plant residues, composts, and manures. We also evaluated FT-NIR for determining the C/N, LIC/N, and BSI/N ratios as indexes of N mineralization in selected organic products. We analyzed 148 organic products for biochemical composition and total C and N. A subset of 10 products was incubated in a sandy soil to determine PMN. The FT-NIR successfully determined lignin and cutin ( LIC) and BSI from r(2), the ratio of prediction to standard deviation, and the ratio error range criteria. The PMN was less closely related to the C/N ratio (r(2) = 0.64) than the BSI/N (r(2) = 0.84) and LIC/N (r(2) = 0.87) ratios. There was some N immobilization at an early stage of incubation when C/N, LIC/N, and BSI/N ratios exceeded 14, 10, and 15, respectively. There is a need to characterize a larger number of organic compounds in the soluble and LIC fractions to improve the BSI equation.