Set up a data logger to record the soil temperatures at the 2,6,10 and 14 inch depths. The area where i set up is in soil that is classified as sandy loam.
 Here are some charts comparing the temps on some selected days. Pay attention on what happened on late 6/9 and early 6/10 to the 2 inch soil temp.

(antelope se half circle 2 6 10 and 14 inch soil temps 6 3 2015.bmp)

(antelope se half circle 2 6 10 and 14 inch soil temps 6 6 2015.bmp)

(antelope se half circle 2 6 10 and 14 inch soil temps 6 9 2015.bmp)

(antelope se half circle 2 6 10 and 14 inch soil temps 6 10 2015.bmp)

(antelope se half circle corn data logger 6 2 2015.jpg)

antelope se half circle 2 6 10 and 14 inch soil temps 6 3 2015.bmp (627KB - 161 downloads)

antelope se half circle 2 6 10 and 14 inch soil temps 6 6 2015.bmp (624KB - 169 downloads)

antelope se half circle 2 6 10 and 14 inch soil temps 6 9 2015.bmp (629KB - 170 downloads)

antelope se half circle 2 6 10 and 14 inch soil temps 6 10 2015.bmp (567KB - 164 downloads)

antelope se half circle corn data logger 6 2 2015.jpg (286KB - 166 downloads)