Abstract
Agriculture consumes more than two thirds of the total freshwater of the planet. This issue causes substantial conflict in freshwater allocation between agriculture and other economic sectors. Regulated deficit irrigation (RDI) is key technology because it helps to improve water use efficiency. Nonetheless, there is a lack of understanding of the mechanisms with which plants respond to RDI. In particular, little is known about how RDI might increase crop production while reducing the amount of irrigation water in real-world agriculture. In this review, we found that RDI is largely implemented through three approaches: (1) growth stage-based deficit irrigation, (2) partial root-zone irrigation, and (3) subsurface dripper irrigation. Among these, partial root-zone irrigation is the most popular and effective because many field crops and some woody crops can save irrigation water up to 20 to 30 % without or with a minimal impact on crop yield. Improved water use efficiency with RDI is mainly due to the following: (1) enhanced guard cell signal transduction network that decreases transpiration water loss, (2) optimized stomatal control that improves the photosynthesis to transpiration ratio, and (3) decreased evaporative surface areas with partial root-zone irrigation that reduces soil evaporation. The mechanisms involved in the plant response to RDI-induced water stress include the morphological traits, e.g., increased root to shoot ratio and improved nutrient uptake and recovery; physiological traits, e.g., stomatal closure, decreased leaf respiration, and maintained photosynthesis; and biochemical traits, e.g., increased signaling molecules and enhanced antioxidation enzymatic activity.
Highlights
Regulated deficit irrigation (RDI) is generally defined as an irrigation practice whereby a crop is irrigated with an amount of water below the full requirement for optimal plant growth; this is to reduce the amount of water used for irrigating crops, improve the response of plants to the certain degree of water deficit in a positive manner, and reduce irrigation amounts or increase the crop’s water use efficiency (WUE)
Water use efficiency (WUE) serves as a key variable in the assessment of plant responses to RDI-induced water stress, because the outcome of using RDI in crop production is to assess the amount of irrigation that can be saved or the crop yield produced per unit of water supplied
Most of the studies that we have reviewed show that the foremost benefit of using RDI is to reduce the amount of irrigation and increase WUE, but crop yield can be increased, maintained, or decreased (Table 1); this has been demonstrated in many crop species such as green gram (Vigna radiata L.) (Webber et al 2006), maize (Li et al 2013), potato (Xie et al 2012), and tomato (Wang et al 2010a), as well as some woody plant species, such as pear–jujube tree (Zizyphus jujube Mill.) (Cui et al 2009a), almond (Prunus dulcis Mill.) (Egea et al 2011), apple (Van Hooijdonk et al 2004), and peach (Prunus persica L) (Geiiy et al 2004)
Summary
2. Definition and main approaches 2.1. Stage-based deficit irrigation 2.2. Partial root-zone irrigation 2.3. Subsurface irrigation or infiltration movement 3. Physiological basis 3.1. Leaf water content 3.2. Stomatal morphology 3.3. Photosynthesis and respiration 4. Biochemical basis 4.1. Plant hormones 4.2. Antioxidation enzymes 4.3. Non-enzymatic substances
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