During the transition seasons as warm and cold air masses battle it out, it is fun to check in on soil temperatures with depth as their response is often interesting. The featured chart presents soil temperatures since 20 November from the ISU Horticulture Farm near Ames showing depths of 4, 12, 24, and 50 inches. Within the soil, the proximity to the ground/air interface (read surface) is important as it takes time for heating from sunshine or warm air masses to penetrate. The diurnal response of the four inch depth value is much more amplified than that of twelve inches. The response is even slower and more muted at deeper depths, but the periods of warming shown at four inches eventually work their way to lower depths! So while the overall trend at the deeper depths is for cooling this time of year, the warm periods above do create bumps along the down-glide.

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