Irrigation Scheduling Strategies for Limited Irrigation Conditions.

When precipitation and irrigation water cannot meet seasonal crop water requirements, the amount and timing of irrigations become critical decision factors for managing crop water stress and optimizing corn (Zea mays, L.) production. The objective of this study was to evaluate the performance of the soil water stress coefficient (K_s) and crop water stress index (CWSI) techniques for estimating actual corn evapotranspiration (ET_a) for irrigation scheduling under water stressed conditions. Non-stressed crop ET (ET_c) was estimated using Penman-Monteith reference evapotranspiration (ET_r) multiplied by a non-stressed crop coefficient (K_c). The two aforementioned indices were used to adjust the non-stressed ET_c for estimating stressed corn ET_a. A field experiment in northeast Colorado considered 3 sprinkler irrigation treatments [opportunity: irrigations occurred according to system capacity; limited: no irrigations during V5 – V10 corn vegetative phases; and drought: 50% of opportunity treatment] and 4 corn varieties, with one being a drought-tolerant hybrid. There were four replications of each treatment combination. Preliminary analyses showed that the K_s tended to over-estimate the level of crop stress, which resulted in under-estimation of ET_a and irrigation water requirements. The CWSI seemed to better represent the water stress levels of the corn crop, but field methods for regularly obtaining crop canopy temperature still needs to be refined for tactical (day-to-day) irrigation scheduling. An improved stress coefficient for use under limited irrigation conditions can help provide better ET_a estimates for irrigation scheduling.