Delayed sowing increases critical density of winter wheat.

Delayed sowing reduces winter wheat productivity and increases the seeding density required to achieve maximum yield. A global analysis of 40 experiments showed an increase in the critical seed rate from 292 to as many as 463 seeds per square meter when sowing occurs 30 days after the recommended time.

The study compiled 658 average yields from experiments conducted in North America, Asia, and Europe. Productivity ranged from 0,3 to 10,5 Mg per hectare.

Seeding and density

The synthesis evaluated the interaction between sowing date and sowing density in winter wheat (Triticum aestivumThe objective included identifying additive, synergistic, or antagonistic relationships between the factors and estimating the critical seed density to achieve 95% of the maximum yield.

Results indicated a predominance of negative additive responses. This pattern occurred in 40% of the combinations evaluated between delayed sowing and increased density. Negative antagonistic relationships appeared in 25% of cases.

A negative additive relationship indicates an absence of interaction between the factors. In this scenario, the usual seeding density is already approaching the critical density needed to maximize yield under delayed planting conditions.

Negative antagonistic relationships indicate partial compensation for the effect of the delay. Increased density raises productivity, but does not fully recover the losses caused by late sowing.

The database compiled 169 combinations of delayed sowing and density. Most showed delayed sowing as the main determining factor in the productive response.

Progressive increase in density

Michaelis–Menten type models estimated a progressive increase in critical density as the delay increases. The critical rate reached 292 seeds per square meter on the normal sowing date. The value rose to 455 seeds per square meter with a delay of 10 to 30 days and reached 463 seeds per square meter with a delay greater than 30 days.

The increase in density raised aboveground biomass, number of ears, and number of grains per area. The weight of one thousand grains remained stable in response to variations in density.

The reduction in yield due to delayed planting was mainly due to a smaller number of ears and lower biomass production. Higher density increased the number of ears per area, but reduced the number of grains per ear, demonstrating a trade-off between yield components.

Further information can be found at doi.org/10.1002/csc2.70252