Tillage and Surface Residue Effects on Soil Upper Boundary Temperatures

The effects of tillage-surface residue interactions on soil upper boundary temperatures are described. 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°C, respectively, between no residue and surface residue treatments for the same tillage condition. Soil surface temperature variation due to the disturbance of soil by tillage for the similar residue cover condition were relatively small. 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. This procedure simplifies the upper boundary temperature data for easy comparison between treatments, seasons, and locations. Comparison of the average normalized soil surface temperature curves suggests that the shape of the daily soil surface temperature curve is slightly different for various tillage and residue interactions, with and without a corn crop. These differences in the average normalized soil surface temperature curves suggest that residue cover delays cooling more than heating of the soil surface. Based on the regression and the average normalized soil surface temperature curves, a procedure is described to estimate the soil upper boundary temperatures for various tillage and surface residue conditions from daily maximum and minimum air temperatures. Application of these soil upper boundary temperatures is in the physically based soil temperature models to estimate the root zone soil temperatures for various tillage and residue management systems with and without a corn crop.