Evaluation of anaerobic biodegradability of forage rice straw fertilized with livestock waste

Fertilizing livestock waste for forage rice production can remove nitrogen and reduce the need for chemical fertilizers. Furthermore, rice straw can be used for biogas production. Here, the growth characteristics of different forage rice varieties in Japanese paddy fields fertilized with liquid cattle waste were investigated. Six experimental plots were established in a paddy field planted with three varieties of forage rice developed for livestock feed. Methane production potential assays were then conducted to investigate the anaerobic digestion characteristics of the stems and leaves of these three varieties. The total methane production potential of the Leafstar variety was higher than that of other varieties, while its lag phase was significantly shorter. Co-digestion of ethanol fermentation residue with Leafstar straw revealed that the NH₄⁺-N concentration decreased as the C/N ratio increased. Additionally, the methane production potential of the mixed substrate was higher than that of ethanol fermentation residue or forage rice straw applied alone. Hence, Leafstar forage rice is a promising variety for establishment of agricultural resource recycling systems in which higher straw biomass can be achieved by applying liquid cattle waste and more biogas can be produced due to the potential for increased methane production.