Evapotranspiration adjustments for deficit‐irrigated corn using canopy temperature: A concept

Sustainability of irrigated agriculture with declining water supplies is a critical agricultural issue in the US Great Plains. Imposing water deficits on crops during noncritical growth periods must be implemented to maximize net economic output per unit of water consumed by the plant. An irrigation timing and amount determination for such a scenario is not a simple straight-forward procedure. Methods that monitor plant stress indicators would appear to be most promising. Several canopy temperature-based irrigation timing techniques exist that determine when to irrigate but do not indicate how much to irrigate. The reference ET-crop coefficient procedure for determining crop ET which is used in fully irrigated crop conditions would be easiest to implement; however the water stress coefficient used in that procedure may not be applicable for prolonged periods of water stress. The objective of this study was to investigate use of a ratio of canopy temperature (Tc) measured over fully irrigated and water-stressed corn (Zea mays L.) as a substitute for the water stress coefficient presently used in the reference ET-crop coefficient concept. Preliminary results indicated that the Tc ratio is a reasonable quantitative water stress coefficient for calculating crop ET under water stress conditions. This ratio allows application of the crop coefficient method for scheduling deficit irrigation. Furthermore the Tc ratio lends itself to hourly incorporation of plant stress effects on crop ET since canopy temperature can be measured continuously throughout the day. Published in 2010. This article is a US Government work and is in the public domain in the USA. RESUME La durabilite de l'agriculture irriguee sous contrainte d'approvisionnement en eau est mise en cause dans les Grandes Plaines americaines. Imposer des deficits en eau des cultures durant les periodes de croissance non-critique doit etre mis en œuvre pour maximiser la marge nette de chaque unite d'eau consommee par la plante. Determiner le moment precis et le volume d'irrigation dans un tel scenario n'est ni simple ni immediat. A cet effet les methodes pour piloter l'irrigation existent basees sur des temperatures de surface de la canopee mais elles ne renseignent pas quant au volume a appliquer. La methode pour determiner le coefficient cultural adapte aux conditions de stress lors de l'estimation de l'evaporation de refernce serait plus facile a mettre en œuvre mais le coefficient ainsi determine ne peut etre applicable pendant des periodes prolongees de stress hydrique. L'objectif de cette etude est d'etudier un indicateur utilisant la temperature du couvert (Tc) d'une culture (Zea mays L.) conduite respectivement a l'evaporation maximale et en condition de stress et qui se substituerait au calcul de l'evaporation de reference avec application du coefficient cultural adapte. Les resultats montrent que l'indicateur base sur la temperature de surface permet de quantifier le stress hydrique et s'applique au pilotage de l'irrigation deficitaire.. En outre cet indicateur se prete a des piloteges a des pas de temps fins puisque la temperature du couvert peut etre mesuree en continu pendant toute la journee. Published in 2010. This article is a US Government work and is in the public domain in the USA.