Determination of Methane Fermentation Yield and its Kinetics by near Infrared Spectroscopy and Chemical Composition in Maize

Abstract

Maize ( Zea mays L.) is the most commonly used substrate for methane production through anaerobic fermentation and is gaining further importance in Germany. Laboratory assays used for the determination of methane fermentation yield (MFY), i.e. the amount of methane produced per unit of dry matter, are complex and costly. Thus, the adoption of near infrared (NIR) spectroscopy, which is already successfully used for fast and cost-effective examination of animal feeds, would remedy this problem. The objectives of this study were to examine the potential of employing NIR spectroscopy to predict MFY as measured in a discontinuous fermenter, investigate the reliability of prediction of parameters related to the kinetics of MFY and compare models based on NIR spectroscopy with that on chemical composition for reliable prediction of MFY. Samples of dried whole plant material from 55 maize genotypes, grown in six environments, were analysed for their MFY using a discontinuous fermentation assay for different fermentation times. Further, chemical composition of the samples was analysed and NIR spectra were measured. Calibration models were developed to predict MFY and related traits based on NIR spectroscopy or chemical composition. Prediction of MFY after a short fermentation time ( R 2 = 0.88 after five days) was better than after complete fermentation ( R 2 = 0.77 after 35 days). Chemical composition models were always inferior to NIR spectroscopy models and showed a strong decrease in performance to predict MFY with ongoing fermentation time. The superiority of NIR spectroscopy is most likely attributable to higher information content in the NIR spectra. The fast determination of MFY by NIR spectroscopy will enable the examination of a larger number of samples and, therefore, allow for the use of MFY in maize breeding for biogas production.