Analysing carbon fractions of growing media by near- infrared spectroscopy

D. Lohr, C. Wöck, S. von Tucher, E. Meinken
Colonisation of peat based growing media by saprophytic fungi is an increasing problem. One important risk factor for excessive fungal growth is biodegradability of organic matter. Especially hydrolysable carbon seems to be a readily accessible carbon and energy source for these fungi. But established chemical methods to analyse hydrolysable carbon are expensive and time consuming. Near-infrared spectroscopy (NIRS) might be a cheap and fast alternative. The dataset consists of various growing media constituents (peat, green waste compost, composted bark, coco pith, wood fibre) and mixtures of peat with one of the listed peat substitutes. NIR spectra were taken of dried and ground samples using a FT-NIR spectrometer. Various pre-processing methods were applied and PCA and PLS models were calculated. As reference values a) hydrolysable carbon was digested with 0.005 M and 1 M HCl, respectively, and measured by ICP-OES and b) total organic carbon (TOC) and total carbon (TC) were analysed with an elemental analyser. Ergosterol as indicator for fungal biomass was determined after inoculation with Peziza ostracoderma and subsequent incubation for 12 days. Coir pith and wood fibre show a different spectral pattern and were removed as outliers. For the remaining samples good calibration models were obtained for both hydrolysable carbon fractions (R2≥0.9, RPD≥2.8, RER≥10) but neither for TOC nor TC (R2<0.8, RPD<2.5, RER<10). Both fractions of hydrolysable carbon predicted by NIRS are highly correlated to ergosterol content after incubation (r≥0.74). Thus, NIRS is a valuable tool to identify growing media carrying a high risk of excessive fungal colonisation.
Lohr, D., Wöck, C., von Tucher, S. and Meinken, E. 2017. Analysing carbon fractions of growing media by near- infrared spectroscopy. Acta Hort. (ISHS) 1168:333-340
NIRS, saprophytic fungi, Peziza ostracoderma, hydrolysable carbon, ergosterol

Acta Horticulturae