With the arrival of spring, Illinois farmers are monitoring soil temperatures for decisions in the field. And the soil temperatures are on the rise.
The ISWS Water and Atmospheric Resources Monitoring (WARM) Program records soil temperatures at 4 and 8 inches under grass at 19 sites across the state. In addition, 4-inch bare soil temperatures are computed to represent a cultivated field. These data are available in map and tabular form for the past 7 days at http://www.isws.illinois.edu/warm/soiltemp.asp.
As of April 6, the 4-inch soil temperatures under grass during the day are into the upper 40s in northern Illinois, the low to mid 50s in central Illinois, and the mid 50s in southern Illinois. At night they are cooling off by about 4 to 6 degrees.
The statewide soil temperatures give a general idea of conditions; however, soil temperatures in an individual field will depend on factors such as soil moisture and tillage practices. Also, soil temperatures at the surface will warm up and cool off faster than in deeper layers.