Biogas potential from forbs and grass-clover mixture with the application of near infrared spectroscopy

•Potential of pure stand forbs as substrates for biogas production is emphasised.•Cutting strategy influenced biogas yields and chemical compositions.•NIRS as a successful tools for predicting biogas yield and plants compositions.•Inclusion of forbs in grassland may potentially lead to higher methane production.

This study investigated the potentials of forbs; caraway, chicory, red clover and ribwort plantain as substrates for biogas production. One-, two- and four-cut systems were implemented and the influence on dry matter yields, chemical compositions and methane yields were examined. The two- and four-cut systems resulted in higher dry matter yields (kg [total solid, TS] ha−1) compared to the one-cut system. The effect of plant compositions on biogas potentials was not evident. Cumulative methane yields (LCH4 kg−1 [volatile solid, VS]) were varied from 279 to 321 (chicory), 279 to 323 (caraway), 273 to 296 (ribwort plantain), 263 to 328 (red clover) and 320 to 352 (grass-clover mixture), respectively. Methane yield was modelled by modified Gompertz equation for comparison of methane production rate. Near infrared spectroscopy showed potential as a tool for biogas and chemical composition prediction. The best prediction models were obtained for methane yield at 29 days (99 samples), cellulose, acid detergent fibre, neutral detergent fibre and crude protein, (R2 > 0.9).