Spatial Patterns of Estimated Optimal Flowering Period of Wheat Across the Southwest of Western Australia

In order to maximize wheat yield, farmers need to match sowing date and cultivar phenology to ensure that flowering occurs within the optimal flowering period, which minimizes the combined impacts of frost, heat and water stress on grain yield. The optimal flowering period is location specific and so far the spatial patterns of optimal flowering period have not been defined. This study conducted a simulation analysis using multiple sowing dates, long-term (1967-2007) and fine-scale gridded (0.05 degrees x 0.05 degrees) climate data. The simulations were used to identify the spatial patterns of the optimal flowering periods (defined as a >= 95 % of the maximum mean yield occurred during sensitive growth periods) across the southwest of Western Australia. The results showed that optimal flowering periods of wheat were mainly determined by the spatial pattern of climate, with the cultivar and soil type playing only a minor role. There were clear geographical patterns of the optimal flowering periods across the wheatbelt of Western Australia, with opening and closing dates of the optimal flowering periods being earlier (23 Jul-30 Sep) in the northeast and later (23 Aug-21 Oct) in the southwest. There was a relatively small difference in the duration of the optimal flowering period across most areas of the wheatbelt. Provided flowering occurs within the optimal flowering period, a slow-developing cultivar sown early would achieve higher yield, due to longer period to accumulate biomass, than a fast-developing cultivar sown late. These result's provide Western Australian growers with knowledge of how to match sowing date and cultivar to achieve flowering within the optimal flowering period.