Greenhouse gas formation during the ensiling process of grass and lucerne silage

Abstract

Silage is an essential global feedstuff and an emitter of greenhouse gases. However, few studies have examined the formation of carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄) during the ensiling process. This study aimed to record the course of gas concentrations in forage during the ensiling process and determine the temporal variation in the (microbiological) formation processes. Grass and lucerne, each with two different dry matter (DM) concentrations (four variants, each n = 3), were ensiled in laboratory-scale barrels (120 L). Gas samples were taken from the headspace of the barrels and analysed using a gas chromatograph. The measurement period included the first 49 days of the ensiling process and the measurement interval was 0.5-48.0 h. For all variants, a rapid increase in CO₂ concentration and a one-time N₂O concentration peak was observed between ensiling hours 36 and 96. Lower DM concentration led to significantly faster CO₂ production (p < 0.05). Lucerne forage and higher DM concentrations led to significantly increased N₂O concentrations (p < 0.05). The extensive measurements demonstrated that butyric acid formation by clostridia contributes to CH₄ formation; thus, lucerne silage had a significantly higher concentration from ensiling day 13 (p < 0.05). Therefore, malfermentation actively contributes to the formation of greenhouse gases. The method described here provides further insights into greenhouse gas formation during the ensiling process and can thus help to improve ensiling research and management.

Keywords: Carbon dioxide; Clostridia; Enterobacteria; Fermentation; Methane; Nitrous oxide.