Soil Temperatures

It's well known that spring fields with significant crop residue left on the surface will warm more slowly than bare soil. However, crop residues help soils resist both warming and cooling trends in the fall - warming more slowly as air temperatures rise, and cooling more slowly when air temperatures fall. This effect will be proportional to the amount of crop residue covering the soil.

The thermal conductivity of a soil is a measure of the rate at which a soil will warm, and is dependent on the soil's composition, texture, and water content. As the water content of the soil increases, so does the rate at which it can warm, as well as the amount of heat it can hold on a per volume basis. While crop residue will reduce the transfer of heat energy from the sun, bare soils, especially bare soils with a high moisture content throughout its profile, will absorb a great deal of heat energy on bright sunny days. Tillage also affects soil temperature. A rough-tilled soil surface exposes much more soil surface area to moving air, resulting in accelerated drying of a soil which may reduce its heat-holding capacity.

Winds also play a role in soil temperature. A warm wind can accelerate the heating of a cold soil and a cold wind can accelerate the cooling of a warm soil. The greater the difference between the air temperature and the soil temperature, the faster heat transfer takes place. So, if you are wondering why your soils are warmer than your neighbors or cooler than the ones down the road, these factors may play a part in it. Every field is different and should be checked at 4 or more inches deep before risking a nitrogen application this fall.