College News

Ag Instructor Vic Martin: Soil Temperature and Plant Growth

Great Bend Tribune
Published March 5, 2023

The drought monitor report as of Tuesday, February 28 indicates an expansion of exceptional drought in Southwest, South central, and part of Southeast Kansas.  On the positive side, Northeast and part of East Central Kansas are no longer even abnormally dry.  Parts of North Central Kansas are still slightly improving (view the map for the United States).  The six to ten-day outlook (to March 7 to 11) indicates a 60 to 70% chance of leaning below normal temperatures and 50 to 60% chance of leaning above normal precipitation.  The eight to fourteen-day outlook (March 9 to 15) indicates a 70 to 80% chance of below normal temperatures and a 33 to 40% chance of leaning to above normal precipitation.  A much more promising pattern than last year.  Just a note, 70 to 80% chance doesn’t tell you how much colder it will be than normal but simply there is a strong likelihood of below normal temperatures.

Why discuss soil temperature?  Most of us know there is a minimum soil temperature for seeds to germinate.  Gardeners right know are preparing to plant cool season crops such as lettuce.  They are waiting to plant seeds requiring higher soil temperatures such as corn.  But there are many important things to consider besides germination. 

Here is a brief, not exhaustive list of other things soil temperature plays a role in.

  • Hard red winter wheat wont flower and produce seed unless exposed to a certain amount of cold temperatures, depending on the maturity of the variety.  This prevents it from flower too early and allows it to avoid the greatest risk of winter type conditions.
  • Many native plant seeds won’t germinate in the spring unless exposed to a certain amount of cold that allows them to break dormancy and germinate.
  • Soil temperature plays a key role in the growth and development of plants after germination.  Too cold or too hot decreases growth and can even lead to plant death.  And the root system is much more sensitive to hot temperatures than the above ground plant structures.
  • Soil temperature determines the rate of evaporation of water from the soil.  And for nutrients like phosphorus that move to the root by diffusion, cold soil temperatures slow down this process and that is why plants may exhibit nutrient deficiencies even with adequate levels in the soil.
  • It also affects water movement in the soil.  The cooler the temperatures, the slower water will flow.  And for nutrients like nitrate and sulfate carried along in the water, it slows uptake.
  • Soil temperature determines the rate of microbial activity in the soil and microbes are responsible for breaking down organic matter into humus and release nutrients as they do such as nitrogen and sulfur.

Naturally, the list could go on.