Lack of terminal water or heat stress facilitates later optimal flowering periods for barley in Australia

Allowing crop flowering to occur within a window that minimises the long-term likelihood of exposure to abiotic stress is a promising but poorly explored pathway for improving yields. Here, our hypothesis was that environments with lower late season (terminal) water or heat stress would have later optimal flowering periods (OFPs) and higher yields, because lower abiotic stress exposure near the end of the growing season would be conducive to greater biomass and grain production. To test this hypothesis, we conducted a genotype (G) × environment (E) × management (M) analysis for barley crops in both short and long season cropping environments. We simulated multiple sowing times of the parameterised genotypes across the Australian cropping zone. The G×E×M showed earlier OFPs (late August to late September) in Western Australia where terminal water and heat stress were higher, and later OFPs (late-October to early-November) in environments that had generally lower late terminal water and heat stress (e.g. Tasmania). Our results show that terminal stresses, such as those associated with severe heat waves and water deficit, have greater deleterious impact on yield potential than frost risk. This is because heat and water deficit tend to truncate the growing season, while OFPs which avoid the risk of frost facilitate longer growing seasons and thus higher yield potential.