Direct seeding into standing stubble is important for winter wheat production. Standing stubble helps to trap snow that insulates crown tissue from cold winter temperatures. Snow cover ensures the soil temperature at the crown (1/2 to 1 inch deep) stays well above killing temperatures, even with air temperatures at -40°C. Optimally for winter survival, stubble needs to hold four inches or more of snow. This amount of snow will prevent soil temperatures from dropping to lethal temperature.
Snow trapped in the stubble not only reduces the risk of winterkill but also improves soil moisture reserves in the spring.
Tall, dense stubble provides optimal snow trapping capability. Canola, barley, oat, flax, or the stubble of a forage crop all consistently provide this type of stubble. Wheat stubble also provides tall dense stubble but is not recommended due to the potential risk for wheat streak mosaic virus. This disease may develop from a “green bridge” created when a previous cereal crop and the emerging winter crop are too close together, allowing the movement and survival of the disease vectoring mites. At least seven to ten days between the dry-down of spring cereal crops and the emergence of winter wheat is necessary to prevent problems with the disease, as the wheat curl mite needs a live cereal plant for a host at all times. Radiant is currently the only winter wheat variety resistant to the wheat curl mite. Crops that do not provide tall dense stubble such as field pea and lentil are not recommended. However, many winter wheat growers seed into these stubbles with an increased risk of winterkill.
Harvest management of the previous crop including cutting height and straw/chaff spreading also plays a role. Producers should strive to minimize stubble disturbance during harvest and subsequent seeding operations.