Yield penalty due to delayed sowing of winter wheat and the mitigatory role of increased seeding rate

Timely sowing is an important agronomic practice that ensures normal seed germination, stable seedling establishment and final yield formation for winter wheat (Triticum aestivum L.). However, delays in sowing frequently occur due to uncontrollable limitations, especially under multi–cropping. Increased seeding rate is recommended to minimize the negative impacts associated with delayed sowing, but the underlying mechanism is still unclear. A 4–year field study was conducted under winter wheat–maize (Zea mays L.) double–cropping system to determine the grain yield penalty and grain quality deterioration due to delayed sowing of winter wheat and to evaluate the potential compensatory role of increased seeding rate. The results showed that grain yield declined by 1% for each day that sowing date was delayed. Such yield penalty could be mainly explained in terms of suppression of crop growth, yield components, leaf area index (LAI) and biomass production. The reduction in yield–determining attributes was mainly caused by some key environmental limitations, i.e., adverse weather factors such as low temperature during crop vegetative growth, shortened duration of various phases of crop development, and elevated temperature during the grain–filling period. Grain protein and starch content were both increased and milled flour (%) was reduced significantly with delayed sowing. Increased seeding rate completely mitigated the yield loss for a one–week delay in sowing and partially compensated for the two–week delay in sowing. For delays in sowing of more than two weeks, increased seeding rate failed to compensate for the yield penalty. Such failure can be explained by the lack in efficiency of increased plant population under higher seeding rate to compensate for reduced biomass production, LAI and grain number under delayed sowing. Other more effective mitigatory options such as varietal selection and development that could sustain high yield even under delayed sowing should be considered for extended delays of winter wheat.