Cultivar and seeding time role in sorghum to optimize biomass and methane yield under warm dry climate

•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.