Agricultural and Biosystems Engineering
When tilling a field there should be a reason for the tillage, whether it's to kill the weeds, breakup a compaction layer, prepare a seedbed, or in an emergency, stop erosion. Regardless of the reason, every tillage operation is going to remove some surface plant residue and expose the soil for some loss of moisture. In a dry year, particularly, as much residue should be left on the surface as possible. This protects the soil surface from erosion and also catches more snow in the winter which in-turn provides good moisture for starting the crop in the spring. As much soil moisture as possible should be retained for next years crop.
Durland, Bob, "Till For a Reason" (2002). SDSU Extension Extra Archives. 5.