However, research shows this does not usually affect crop yields if good direct seeding practices are followed. Conventionally tilled soils in the Black soil zone average about 1C warmer at the 5 cm depth, but can be as much as 3C warmer for a brief periods during some springs. The advantage usually lasts until mid or late June, when the crop canopy has fully established. The cooler soils under direct seeding are mainly due to the crop residue layer on the soil surface. Data from the Alberta Reduced Tillage Initiative Demonstration Farm at Red Deer show that thicker residue layers result in cooler soils during the spring.
Crop residue reflects sunlight and insulates the soil from the air.
Thicker layers provide better insulation. While this protects direct seeded soils from extreme seasonal temperature changes, it also slows spring warming. During daytime heating, direct seeded soils tend to not warm as much as conventionally tilled soils, but daily minimum temperatures are similar. This suggests that much of the additional heat gained each day in tilled soils is lost at night. Some evidence suggests that this heat loss may warm the seedlings, making overnight cooling and frost risk less severe in tilled soils than in direct seeded soils.