Simulating the effects of weather variables and soil water potential on a corn canopy temperature

The effect of atmospheric vapor pressure deficit (VPD) on canopy-air temperature differnce (δT) of corn (Zea mays L.) is simulated using a soil—plant—atmosphere model together with weather data for several clear-sky days. Considering empirical dependence of stomatal resistance of corn on the leaf water potential and insolation, the model finds an analytic solution for the leaf water potential which satisfies Monteith's and van den Honert's equations for transpiration. The simulated leaf water potentials are compared with observations. For a large portion of the daylight period a near-linear relationship between δT and VPD is found at various soil water potentials. Among weather variables, the air VPD appears to be the most important factor affecting δT for unstressed canopies. With decreasing soil water potential the sensitivity of δT to wind speed increases. The effect of differing rooting densities on δT is also studied. As the rooting density increases the δT values decrease, indicating that δTv. VPD relationship could change with crop age and the soil strength conditions affecting the root growth.