When it comes to the soil temperature, it depends on what you are planting. Shannon Chant is a crop extension specialist with the Saskatchewan Ministry of Agriculture.
She explained for most crops, the ideal temperature is around 10° Celsius. However, if you want to get going a bit earlier, pulses, some peas, lentils and chickpeas, desi's anyway, are okay around 5°. For some others, you may want to wait.
“Chickpeas, dry beans, and soybeans, you should really wait until about that 10°,” Chant elaborated. “For canola and flax, they can germinate as low as 2° Celsius, flax, 3-4°, and cereals at 4 to 5°, but that may mean they are not coming up as good as they could.”
While the sun has been shining, the air temperature doesn’t necessarily affect the soil temperature. Instead, sunshine is the biggest contributor to warming up the soil.
Chant recommends taking the temperatures from various parts of where you will be seeding, ideally, taking one reading in the morning, and a second later in the day. It is also best to take the temperatures at the depths where the crop will be seeded.
Another factor for those who are getting into the field a little earlier is the risk of frost and cold temperatures. Chant explained for pulses or cereals, they start with their growing point under the ground, so they can handle a bit more frost compared to canola, flax or mustard.
“Cereals and pulses are a bit safer option to seed first if you want to get going and there’s a possibility of frost,” Chant added.
Source : Discoverestevan