Is the crop evapotranspiration rate a good surrogate for the recommended irrigation rate?

Abstract

Numerous methodologies and technologies of varying levels of sophistication for irrigation rate determination have been developed over the years to address limited irrigation water availability and optimize water productivity. Crop evapotranspiration is currently evaluated mostly according to the FAO56 approach, which has been augmented in recent years with remote sensing of correlated plant indices. When no other information is available, the evapotranspiration rate does give an indication of the optimal irrigation rate in some circumstances. However, in many other circumstances discussed in this short communication, replenishing the soil with crop evapotranspiration either substantially overestimates or underestimates the optimal, physiological (agronomical/economical) irrigation rate. Consequently, this note raises doubts and opens a discussion about the extensive reliance on the evaluated crop (potential or actual) evapotranspiration rate for recommending an optimal irrigation rate (irrigation dose/irrigation amount).