Abstract
•Study of 5 sorghum cultivars × 3 seeding times for CH4 production in Pakistan.•Late seeding, 23% loss in dry biomass yield but no variation in specific CH4 yield.•Cultivar differences in biometry, composition and yield reflect on CH4 yield.•Slight advantage of dual-purpose vs. fibre genotypes in biomass but not CH4 yield.•Early seeding and best dual-purpose cultivars enhance CH4 production in Pakistan.
Biomass sorghum increasingly constitutes the feedstock for methane production. Optimization of crop management for this use is far from being achieved under warm dry climate. To fill the gap of knowledge, five cultivars of Sorghum bicolor were cross combined with three seeding times (ST) at 20-day intervals from 1st May 2016 and 2017, in a field experiment conducted in Pakistan. Late vs. early seeding determined a 23% loss in dry biomass yield (DBY), but no variation in specific methane yield (SMY). Therefore, methane yield per hectare (MY), their product, staged a 22% loss with late vs. early seeding, reflecting DBY loss. Biometric and compositional changes were shown in late vs. early seeding: smaller plants with lower protein, sugar and fibre content, associated with a hastening in crop development despite non-limiting ambient conditions until maturity. This comprehensive effect explains the yield reductions incurred by late seeding in this and other studies where irrigation could fully compensate lack of precipitation during crop growth. The five cultivars, three of which being dual-purpose genotypes (grain and biomass), and the other two fibre genotypes, staged significant DBY, SMY and MY differences (-28%, -14% and -16%, respectively) between worst and best performing cultivar. Significant seeding time × cultivar interactions indicate a slight advantage across seeding times for dual-purpose vs. fibre genotypes in DBY, whereas in MY none of the two groups clearly prevailed. Results obtained in this experiment complement previous outcomes with cultivars and harvest times, supporting bio-energy growth under warm dry climatic conditions.