This spring was characterized by cool soil temperatures. Soil temperatures were warming up rapidly at the end of April and early May. However cool conditions and snow showers occurred at the start of May. Minimum soil temperatures for wheat to germinate is 5C. However at this temperature emergence takes up to 21 days from a 1 inch seeding depth. Soil temperatures decreases with depth and wheat takes longer to emerge when seeded deep. Work done at the Indian Head Research Station indicated that soil temperatures could easily fall below 5 C due to adverse weather conditions even though it had reached 5 C. However when soil conditions reach 10 C they did not fall below 5 C
Measuring soil temperatures involves taking the temperature at the depth of seeding. Temperatures should be recorded early in the morning when the soil is at its coolest temperature and later in the afternoon to see how much it has warmed. The coolest temperature recorded should be used as a guideline in making the decision as to when to start seeding.
At the Wilkie direct seeding site May 10, the day of seeding, soil temperatures were at approx. 5 C in the morning. By afternoon the temperature had rose to approx. 10 C. the following three days temperatures cooled off coupled with cold rain and snow showers. Soil temperatures stayed in the 5 to 7 C range. Wheat seeded at the one inch depth did not emerge until May 24 approx. 14 days after seeding. Had the wheat been seeded deeper it would have been more susceptible to seed rots, root rots and possible herbicide injury from preemergents.
Another factor in how fast the soil warms is the texture and the amount of moisture that is present. The soil at Wilkie is a loam soil. Clay soils east of North Battleford were 2 - 3 C colder than the soil at Wilkie due to their heavier textures and higher moisture contents.
Soil temperatures on worked summerfallow were similar to standing stubble this spring. Emergence of wheat was not noticeably faster on these fields when seed at the same depth. Worked summerfallow had wider swings in their temperatures due to the lack of an insulating effect from standing stubble.
Measuring soil temperatures can be a useful tool when making the decision to start seeding. Tracking your soil temperatures is another crop management tool that should be used to evaluate the risk in early seeding.