Abstract
The increasing world population and expected climate scenarios impel the agricultural sector towards a more efficient use of water. The scientific community is responding to that challenge by developing a variety of methods and technologies to increase crop water productivity. Precision irrigation is intended to achieve that purpose, through the wise choice of the irrigation system, the irrigation strategy, the method to schedule irrigation, and the production target. In this review, the relevance of precision irrigation for a rational use of water in agriculture, and methods related to the use of plant-based measurements for both the assessment of plant water stress and irrigation scheduling, are considered. These include non-automated, conventional methods based on manual records of plant water status and gas exchange, and automated methods where the related variable is recorded continuously and automatically. Thus, the use of methodologies based on the Scholander chamber and portable gas analysers, as well as those of systems for measuring sap flow, stem diameter variation and leaf turgor pressure, are reviewed. Other methods less used but with a potential to improve irrigation are also considered. These include those based on measurements related to the stem and leaf water content, and to changes in electrical potential within the plant. The use of measurements related to canopy temperature, both for direct assessment of water stress and for defining zones with different irrigation requirements, is also addressed. Finally, the importance of choosing the production target wisely, and the need for economic analyses to obtain maximum benefit of the technology related to precision irrigation, are outlined.
Highlights
Group on Irrigation and Crop Ecophysiology, Instituto de Recursos Naturales y Agrobiología (IRNAS, CSIC), Academic Editors: Arturo Alvino and Maria Isabel Freire Riberiro Ferreira
Most authors using thermal images taken from unmanned aerial vehicles (UAVs) and planes reported robust relationships conductance and stem or leaf water potential [56,64,65], and claimed that the approach was suitable between the derived CWSI and main physiological variables related to water stress, such as stomatal for characterizing plant water status variability in woody crops
Comparative studies of the ZIM system vs. Scholander-type chambers have been made by Westhoff et al [166] for grapevines, by Rüger et al [165] for eucalyptus, avocado, grapefruit, beech and oak, and by Ben-Gal et al [170] and Fernández et al [49] for olive. These studies showed that the ZIM system is robust, relatively inexpensive, and suitable for automatic and continuous recording under field conditions for long periods of time, and that it has a great potential as a water stress indicator in vineyards and fruit tree orchards
Summary
Precision agriculture began in the 1960s with the use of geographic information systems (GIS), probably the first precision farming tools developed. The most demanding steps for PI, i.e., on the wise choice of the irrigation strategy, the method for the assessment of water stress and for irrigation scheduling, and the definition of the most appropriate production target, are considered. Regulated deficit irrigation is challenging because it requires both a sound knowledge of the both a sound knowledge of the physiological response of the crop to water conditions and precise physiological response of the croplevels to water and precise assessment plant water stress assessment of plant water stress alongconditions the growing cycle [5]. The target production to achieve thebalance most between profitable and oiloil quality the oil same time that a long productive the productive orchard waslife ensured reducing between yieldatand quality at the same time thatlifea of long of thebyorchard was problems derived from competition for light among trees. Fernández et al [6] and Padilla-Díaz et al [7]
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