Agronomic adaptations to heat stress: Sowing summer crops earlier

Summer crops are exposed to heat and drought stresses at critical stages during and after flowering, and their intensity and frequency are likely to increase with climate change. Agronomic stress avoidance offers the opportunity to temporally separate critical crop stages from heat and drought events. However, it might require sowing cold-sensitive summer crops earlier into colder than recommended soil temperatures. There is a need to understand how cold is too cold to sow summer crops early in late winter as well as what are the yield benefits and risks. Here, we quantify the likely benefits and trade-offs of sowing sorghum, a summer cereal, earlier to adapt to the increased frequency and intensity of heat and water stresses during flowering and grain filling. Two years of multi-environment (n=32) genotype by management trials were conducted across the main sorghum growing regions of Australia. Environments (E) consisted of the combination of years, sites, three times of sowing (early, spring, and summer), and the use of supplementary irrigation. At each E a factorial combination of four plant populations (M) and eight commercial sorghum hybrids (G) were sown with three replications. Crop growth and yield components were measured, and the APSIM model was used to simulate all trials and treatments to quantify risks and derive insights into functional relationships between simulated and measured environmental covariates, and measured crop traits. The tested hybrids showed small differences in cold tolerance during crop establishment. Across the tested environments, the G×M combinations produced up to 60 % variation in treatment yields across environment yields, which varied between