Evapotranspiration and Plant Water Stress Measurements as the Driving Standard for Agricultural Irrigation

Dear Colleagues,

This Special Issue of Water will be focused on several topics that we have selected based on the following rationale:

1. With irrigation accounting worldwide for about 70% of all water use, the proper modelling of plant water requirements is a critical issue for water management in agriculture, but its accuracy is highly dependent on the availability of quality data.
2. Improvements to the existing algorithms for estimating ET are based on ET measurements. These measurements, when applied to tall and/or deep-rooted permanent crops, require expensive equipment, sophisticated know-how, and high commitment from researchers.
3. Furthermore, reliable evapotranspiration (ET) estimates are more challenging for permanent crops, especially when subjected to water stress, i.e., deficit-irrigated or rainfed crops.
4. Conversely, a water stress diagnosis is necessary for the interpretation and therefore the best use of such water flux measurements.
5. Ensuring proper irrigation scheduling requires more than a stress indicator that simply reacts to water stress. Instead, an identified threshold or stress function must be established and applied, allowing a transfer in space and time under identical circumstances. This ensures that the meaning of the threshold or stress function remains consistent, making it easier to adapt and manage irrigation schedules effectively.
6. The analysis of survival mechanisms regarding water stress (hydraulic redistribution) and the derived new concepts around functional root volume are critical to our understanding of plant water use in almost-rainfed stands, mainly in Mediterranean and semi-arid climates. 
7. We do not yet have sufficient useful data from measuring ET and quantifying and understanding stress levels. More reliable field data, sound interpretations, and the good communication of results are necessary in order to best aid the scientific/engineering community.

Considering these points, we welcome the submission of manuscripts for this Special Issue addressing the following topics: 

• measurements of evapotranspiration;
• reference information to be used for modelling and reviewing crop coefficients;
• assessment of plant water stress;
• use of crop water stress measurements and threshold establishment to schedule deficit irrigation;
• resilience to water stress in a plant/soil continuum.

Prof. Dr. Teresa Afonso do Paço
Prof. Dr. Maria Isabel Freire Ribeiro Ferreira
Guest Editors

Prof. Dr. Joao Rolim Lopes
Guest Editor Assistant

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