Predicting Temperatures of Bare and Residue Covered Soils With and Without a Corn Crop

Models are described to predict the upper boundary and root zone temperatures for bare and various residue-covered soils with and without a growing corn (Zea mays L.) crop. The model for predicting upper-boundary temperatures is based on the assumption that the difference between hourly air temperature at the 2-m height and the soil surface temperature follows a sine function. The root zone temperature model, on the other hand, is based on the numerical approximation of heat flow equation and uses the estimated upper-boundary temperatures as an input for its prediction. Inputs to the model are hourly air temperature at the 2-m height, daily maximum and minimum temperatures under the soil surface, initial soil temperature, and thermal diffusivity profiles. Thermal diffusivities are estimated from soil mineralogy, organic matter percentage and bulk density data, and field measurements of matric potential. Ninety-five percent of the predicted hourly upper-boundary temperatures varied within −8.9 to 8.9°C and −3.2 to 4.4°C of the measured upper boundary temperatures for bare and corn with 50% residue-covered soil surfaces, respectively. However, the hourly differences between the predicted and measured root zone temperatures were smaller when these estimates of the upper boundary temperatures were used in the numerical analysis. Daily predictions of root zone temperature using estimated upper boundary temperatures were within 2°C of the measured value over most of the growing season. Differences between the predicted and measured root zone temperature were large only when measured root zone temperatures were greater than 28°C. Differences between measured and predicted root zone temperatures decreased with increase in (i) plant or residue cover at the soil surface and (ii) soil depth. Daily root zone soil temperature predictions from the model will be useful for modeling the soil-plant-atmospheric continuum, where daily soil temperature values are required, but an error of ± 3°C can be tolerated. Examples of application are modeling nitrogen transformations in soils and crop yield predictions. The present approach has an advantage in that it uses hourly air temperatures measured at a weather station; these values also are used as input for various crop growth models.