Abstract: A constant contact reference wheel system includes a vehicle carrying a water reservoir, and a constant contact reference wheel. The constant contact reference wheel includes a frame having a first end and a second end, an attachment mechanism carried by the first end removably coupling the frame to the vehicle, a wheel structure having a rim for rolling contact with a soil surface, and a reference cell carried by the frame. A water pathway extends from the water source to the rim. The rim exudes water for contact with the soil surface, and the reference cell is in fluid communication with the water pathway.