Determination of chemical and biological properties of composts using near infrared spectroscopy
MICHEL, K., BRUNS, C., TERHOEVEN-URSELMANS, T., KLEIKAMP, B. and B. LUDWIG
J. Near Infrared Spec., 14:251-259
Successful use of compost to maintain plant health and soil fertility requires consistent monitoring of compost quality. For this purpose, near-infrared spectroscopy (NIRS) might be a useful alternative to standard procedures which are often time-consuming and laborious. Ninety-eight yard-waste compost samples were analyzed by conventional methods and NIRS. Reference analysis included the determination of age, organic C (Corg) and total N (Nt) contents, C/N ratio, microbial biomass (Cmic), the ratio of Cmic to organic C (Cmic/Corg), basal respiration, metabolic quotient (qCO2), hydrolysis of fluorescein diacetate (FDA-HR), specific enzyme activity, i.e. FDA-HR related to Cmic, and suppression of pathogens. All samples were scanned in the visible light and near-infrared region (400 - 2500 nm). Cross-validation equations were developed using the whole spectrum (first and second derivative) and a modified partial least-square regression method. NIRS predicted basal respiration and age successfully (RPD (ratio of standard deviation and standard error of cross-validation) was 4.3 or 2.9, respectively). All other properties, i.e. Corg and Nt contents, C/N ratio, Cmic, Cmic/Corg, qCO2, FDA-HR, specific enzyme activity and suppression of pathogens at an inoculation level of 5 ‰ related to rating or fresh weight, respectively, were predicted moderately successful (1.4 £ RPD £ 2.0). However, the coefficients of determination for specific enzyme activity and suppression of pathogens related to fresh weight were rather low (r² = 0.49 and 0.47, respectively). The results presented indicate that NIRS is capable to determine important compost quality parameters. However, further research is needed concerning the basis of and limitations for the determination of specific enzyme activity and suppressiveness by NIRS.