Photoperiod Sensitivity Modifies the Response of Methane Yield and Water Productivity to Water Supply in Sorghum

Water availability is a major constraint for biomass-based bioenergy production, yet its interaction with sorghum photoperiod sensitivity on methane productivity remains poorly understood. This study evaluated the effects of water supply and photoperiod sensitivity on biomass yield (BY), specific methane yield (SMY), methane yield (MY), and methane water productivity (MWP) using five sorghum hybrids grown under rainfed and irrigated conditions across three growing seasons in Argentina. Photoperiod-sensitive (PS) hybrids produced greater biomass than photoperiod-insensitive (PI) hybrids, resulting in higher MY and MWP across environments. Biomass yield increased with total water supply, although PS hybrids exhibited a non-linear response, whereas PI hybrids showed a more stable pattern. SMY declined slightly with increasing water availability, indicating that moderate water deficit improved methane conversion efficiency but not sufficiently to compensate for reductions in biomass production. Consequently, BY remained the dominant determinant of methane productivity across the evaluated water gradient. MWP decreased with increasing water supply, highlighting a trade-off between maximizing methane production per unit area and per unit of water supplied. The results demonstrate that photoperiod sensitivity strongly influences sorghum responses to water availability and support the selection of PS hybrids for maximizing methane production.