Community level physiological profiling as a tool to evaluate compost maturity: a kinetic approach

Although often used for soil studies, community level physiological profiles (CLPPs) have been rarely applied to compost, probably for the lack of standardized methodology. Recently, however, CLPPs have been proposed as a tool to assess the degree of maturity of compost. One of the major problems is that the rate of colour development is a non-linear process related to both time and inoculum density. The aim of this work was to investigate the suitability of data interpretation based on the kinetics of colour formation. Extracts from compost samples of different age were diluted in four different dilutions and inoculated into Biolog Ecoplates. Optical density (OD) in wells was measured (592 nm) every 8 h for 7 d. Kinetic parameters were estimated by fitting the curve of OD vs. time to a logistic growth equation. Principal component analysis (PCA) clearly showed an effect of dilution on CLPPs, but the pattern of ordination of compost by age groups was generally the same in the different dilutions. If parameters were grouped for classes of compounds, discriminant analysis was able to separate samples of different age. In particular, phenolic compounds were the class of components that most significantly contributed to sample classification.