TILLAGE AND SURFACE RESIDUE EFFECTS ON SOIL UPPER BOUNDARY TEMPERATURES.

Regression curves are developed between the maximum and minimum soil surface temperatures vs. maximum and minimum air temperatures at the 2-m height. Soil surface temperature variations between various residue and tillage treatments were mainly due to the change in surface residue cover. During fall and spring, the maximum temperature differences were 12 and 19 degree C, respectively, between no residue and surface residue treatments for the same tillage condition. During the growing season, maximum and minimum soil surface temperatures under corn canopies were approximately the same for all tillage-residue interactions. A procedure to normalize diurnal upper boundary temperatures with respect to daily maximum and minimum soil surface temperatures is suggested.