When soil conditions are dry, the temptation often exists to seed winter wheat deeper than the recommended 1 inch depth. However, the recommendation remains the same – don’t seed deeper than 1 inch. A study done from 1983 to 1986 by Agriculture Canada (Indian Head Research Farm) compared two seeding depths – shallow (0.5 to 1 inch) and deep (1 to 2 inch) – and found seeding shallow at the recommended date is necessary to optimize plant establishment in the fall, minimize the risk of winter damage, and maximize yield potential of no-till winter wheat.
Under dry conditions, importance of seeding depth has an even larger influence on plant establishment. Rainfall simulation studies have shown that winter wheat seeded into a dry soil on the optimum seeding date will successfully establish with as little as 1/3 inch of rain. However, when seeding depth is increased to 1.5 inches, at least 1/2 inch of rain is required to establish winter wheat when soil temperatures are above 15°C.
So why the recommended 1 inch seeding depth? Winter wheat has a very short coleoptile, which is the extension of the seed embryo that pushes its way through the soil to the surface. The coleoptile is limited in its length by both genetics and by the energy stored in the seed. If the seed is planted too deep, it can deplete its stored energy before it reaches the surface. When the seed energy reserve is depleted, early growth and development can be inhibited as the plant struggles to accumulate sufficient energy reserves in the crown tissue prior to freeze-up. Insufficient crown development can result in reduced winter survival, poor weed competition, late maturity and lower yield potential. So although winter wheat seeded deeper than 1 inch may look okay after emergence, the ability to cold acclimate and survive the winter is reduced and may also impact yield potential the following year.
Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture