Drought and Nitrogen Stress Effects on Maize Canopy Temperature.

Water scarcity is a major threat to the sustainability of irrigated agriculture. Management practices, such as limited irrigation, that seek to maximize the productivity of a limited water supply are critical.  Remote sensing of crop canopy temperature is a useful tool for assessing crop water status and for more precise irrigation management. However, there is potential that nutrient deficiencies could compound the interpretation of water status from leaf temperature by altering leaf color and radiation balance. This paper evaluates whether nitrogen fertility status of maize interacts with remotely sensed leaf temperature under full and limited irrigation.  Replicated studies were conducted using maize grown in both the greenhouse and the field. The greenhouse study consisted of combinations of full and limited irrigation and sufficient and deficient nitrogen levels, while the field study consisted of combinations of full, limited, and drought irrigation and sufficient, sufficient-delayed, and deficient nitrogen levels. In the greenhouse, leaf chlorophyll concentration and leaf area were reduced moderately by limited irrigation and more so by N deficiency. For most observations in the greenhouse, the remotely sensed leaf temperatures were affected by irrigation, but not by N level. With limited irrigation, leaf temperature averaged 29.0 C, compared to 27.9 C for full irrigation, illustrating the utility of canopy temperature in detecting water stress and that the measurement was not confounded by N status. On three days, leaf temperature was observed to be greater for plants with sufficient N than for plants that were N deficient.  These temperature differences were related to water stress but not to leaf color. Since these results suggest that plants with sufficient or excess N may experience more drought stress in water limited scenarios, N fertilizer management may be a critical factor in improving water productivity under drought conditions.