2Deficit irrigation is one of the irrigation management methods that is used to increase Water Use Efficiency. Considering the internal plant adaptability characteristic to water shortage, Partial Root Drying method has been introduced in recent years. In this field research improvement of Water Use Efficiency for Soybean was determined. This experiment which was conducted at four furrow irrigation treatments at the Research Field of Tehran University in Karaj in 2008, consists of full irrigation (100% soil moisture deficit compensation), conventional deficit irrigation at 50 and 75 percent soil moisture deficit compensation and Partial Root Drying at 50 percent soil moisture deficit compensation with three replications. The amounts of irrigation used were exactly compensation level (negligible loss). Results indicated that Water Use Efficiency according to Duncan's Multiple Range Test at the five percent level of probability there was a significant difference between Partial Root Drying treatment (PRD50%) and conventional deficit irrigation treatment at fifty percent soil moisture deficit compensation (DI50%),. Water Use Efficiency in PRD50% compared with DI50%, DI75% and full irrigation increased by 48.3%, 61.9% and 70.1% respectively.

Deficit irrigation is one of the irrigation management methods that is used to increase Water Use Efficiency. Considering the internal plant adaptability characteristic to water shortage, Partial Root Drying method has been introduced in recent years. In this field research improvement of Water Use Efficiency for Soybean was determined. This experiment which was conducted at four furrow irrigation treatments at the Research Field of Tehran University in Karaj in 2008, consists of full irrigation (100% soil moisture deficit compensation), conventional deficit irrigation at 50 and 75 percent soil moisture deficit compensation and Partial Root Drying at 50 percent soil moisture deficit compensation with three replications. The amounts of irrigation used were exactly compensation level (negligible loss). Results indicated that Water Use Efficiency according to Duncan's Multiple Range Test at the five percent level of probability there was a significant difference between Partial Root Drying treatment (PRD50%) and conventional deficit irrigation treatment at fifty percent soil moisture deficit compensation (DI50%). Water Use Efficiency in PRD50% compared with DI50%, DI75% and full irrigation increased by 48.3%, 61.9% and 70.1% respectively.

Available fresh water resources are subjected to an ever-increasing pressure due to extensive agricultural water demand for irrigated lands. A long-term perspective in shortage of fresh water resources, especially in arid and semi-arid area, highlights an urgent solution for innovative irrigation strategy and agricultural water management. This paper is a review on the wide applications of the Partial Root-zone Drying irrigation (PRD) on diverse plant species. The PRD irrigation is a novel improvement of deficit irrigation in which half of the Root zone is irrigated alternatively in scheduled irrigation events. In the last decade, scientists across the world, especially from arid to semi-arid countries, have extensively evaluated this irrigation as a water-saving irrigation strategy on agronomic and horticultural plants. This review paper focuses on the physiological and morphological aspects of PRD on plants and its ultimate impact on yield and water productivity. Overall, under limited water resources where water is precious, PRD is a viable irrigation option to increase water productivity while margining the yield, rather than only increasing the economic yield without concerning the value of water in limited water environments.

Due to the increased water consumption and the depletion of water resources, deficit irrigation is an optimal strategy for cultivation, which is usually applied by utilizing the methods of Deficit Irrigation (DI), Regulated Deficit Irrigation (PRD), and Partial Root-zone Drying Irrigation (PRD). In the PRD method, just one side of the plant is irrigated in each irrigation interval. Under these conditions, in the part of the irrigated plant, the Roots absorb enough water and grow, so that there is no change in the amount of the plan’s photosynthesis. There are some models, including WOFOST (Van Diepen et al., 1989; Boogaard et al., 1998), EPIC (Jones et al., 1991), AquoCrop (Steduto et al., 2009), and STICS (Brisson et al., 2003), that can simulate crop yield under different soil conditions, Climates, irrigation schedule, and agricultural managements (Hashemi et al., 2018). These models simulate PRD irrigation, such as the DI method. Daisy is the first model, differentiating the gained results between the two methods (Hansen et al., 1990; Hansen et al., 1991); a semi-experimental model that considers the Richards equation (Richards, 1931) to simulate the soil water content and the experimental equations to simulate crop yield parameters. The PRD sub-model in the Daisy was developed and upgraded based on the data gained from potato cultivation under PRD irrigation (Liu et al., 2008; Plauborg et al., 2010). Since this sub-model was developed only for the potato, the aim of the present study was calibration and validation of two parameters; stomatal slop factor (m) and specific leaf weight modifier (LeafAIMod) in the PRD sub-model, to run the Daisy model to simulate sunflower under the PRD irrigation.

Increasing the water use efficiency in crop production is an important issue today. An experiment was conducted in 2009in order to evaluate the corn reaction to Partial Root zone Drying at Fars province. Treatments consisted of four irrigation levels(control, alternative furrow irrigation during whole season, alternative furrow irrigation until flowering then full irrigation andfull irrigation until flowering then alternative furrow irrigation after flowering) and three potassium levels (0, 100 and 200 kgha-1 potassium sulfate). The treatments were arranged as split plots (Irrigation regimes as main plots and K fertilizer levels assub plots) and the data was analyzed based on a randomized complete blocks design with three replications. The results showedthat irrigation had significant effects on grain yield, water consumption, grain weight and grain number per ear. The highestgrain yield obtained in control irrigation but it was not significantly different from alternative furrow irrigation until flowering.The lowest water consumption was observed in alternative furrow irrigation until flowering treatment. Potassium treatmentshad significant effect only on grain yield. In conclusion the results suggested that with alternative furrow irrigation water usereduced and water use efficiency increased compared to conventional methods.

Deficit irrigation is one of the ways to increase water productivity in irrigated lands. This study was conducted as a split plot experiment in a randomized complete block design with three replications on flat tomato cultivar at the Research Farm of Ferdowsi University of Mashhad, Iran, during the 2018 cropping season. Treatments included three irrigation methods including; usual irrigation, fixed Partial Root-zone Drying and alternative Partial Root-zone Drying as main plots and three levels of deficit irrigation (50, 75 and 100% of field capacity) as subplots. Results show that the highest and lowest concentration photosynthetic pigments observed in the alternative Partial Root-zone Drying and the fixed Partial Root-zone Drying respectively. Maximum plant height (68. 8 cm) was observed in fixed Partial Root-zone Drying. Results show that, the maximum leaf area index (2. 15), stem dry weight (76. 5 g. plant-1), leaf dry weight (72. 6 g. plant-1) and fruit yield (4. 50 kg. m-2) was found in 100% field capacity. According to the results of the present study, the best result observed in usual irrigation, fixed Partial Root-zone Drying and alternative Partial Root-zone Drying respectively. Fruit yield in fixed Partial Root-zone Drying was more than the alternative Partial Root-zone Drying method.

Considering the limited water resources in arid and semi-arid climate of Iran, deficit irrigation is one of the strategies for efficient use of water and increasing water use efficiency in agricultural districts. In order to study the effects of deficit irrigation on the quantitative traits of Thymus vulgaris L., an experiment was conducted in Kerman Municipality seedling production station in 2016. The experimental treatments were arranged as randomized complete block design with three replications. The irrigation regimes consisted of full irrigation (FI-100), regulated deficit (RDI75% and RDI55%) and Partial Root zone Drying irrigation (PRD75% and PRD55%). The results showed that the highest herbage dry weight (1670. 6 kg/ha) and leaf area index in different stages of growth were produced by full irrigation treatment, while no significant difference between this treatment and PRD75 was observed. Also, the highest number of shoots (64. 4) and plant height (39. 4 cm) were produced by full irrigation treatment and there was significant difference between this treatment and other treatments. However, the highest water use efficiency (0. 66 kg/m3), Root fresh weight (4. 5 g), Root depth (15. 8 cm) and Root volume (2. 8 cm3 per plant) appeared in PRD75. Therefore, 75 percent water replacement in Partial Root zone Drying irrigation treatments, in addition to saving water consumption, provides better use of soil moisture and sunlight. Thus, this treatment can be considered as suitable approach to cope with the water crisis and achieve a sustainable agriculture.

The use of procedures in crop production that improve water use efficiency and reduce water consumption is an important issue. An experiment was conducted in 2009 in order to evaluate the corn (SC704) reaction to Partial Root zone and potassium application at Fars province. Treatments consisted of four irrigation levels (control, alternative furrow irrigation during whole season, alternative furrow irrigation until flowering then full irrigation and full irrigation until flowering then alternative furrow irrigation after flowering) and three potassium levels (0, 100 and 200 kg ha-1 potassium sulfate). The treatments were arranged as factorial experiment based on a randomized complete blocks design with four replications. Corn density was 7 plants/m2.The results showed that irrigation had significant effects on grain yield, water consumption, seed weight, seed per row and grain number per ear. The highest grain yield obtained in control irrigation but it was not significantly different from alternative furrow irrigation until flowering. The lowest water consumption was observed in alternative furrow irrigation until flowering treatment. Potassium treatments had significant effect only on seed weight. Application of 200 kg/ha potassium had the highest seed weight. In conclusion the results suggested that with alternative furrow irrigation water use reduced by 15.61% compared to conventional methods.

In order to study the effects of deficit irrigation on yield of tomato, an experiment was conducted in Jiroft. The experiment treatments were arranged as randomized complete block design with three replications. The irrigation regimes consisted of full irrigation, regulated deficit and Partial Root zone Drying irrigation (RDI75, RDI55). The results showed that deficit irrigation resulted in water saving at the rates of 16%-34%. The highest yield (202. 65 ton/ha) was produced by full irrigation. There was no significant difference between yield and fruit weight of full irrigation treatment and 75% water replacement in Partial Root zone Drying. The highest water use efficiency was 45. 6 kg/m3 obtained in 75% water replacement in Partial Root zone Drying. Also, despite the same water consumption of 75% water replacement in Partial Root zone Drying and regulated deficit, yield was decrease 16. 1%. Therefore, it can be concluded that 75% water replacement in Partial Root zone Drying, which resulted in a non-significant decrease of yield and while resulting in a 25 % decrease in water use and increased 14% of water use efficiency, would be a promising water-saving method as in Jiroft.

Irrigation management is one of the most important factors affecting the development and expansion of the plant Root. The aim of this study was to investigate the effect of different deficit irrigation treatments on the Root characteristics of fodder maize (KSC 704) in surface drip irrigation system. This research was conducted in agricultural research center of Khorasan Razavi during the 2014 growing season. A factorial experiment based on randomized complete blocks design with nine treatments and four replications was carried out. Treatments included full irrigation (FI), deficit irrigation (DI) and replacements of 80 and 60% of total water requirement, Partial Root zone Drying (PRD) at 100, 80 and 60% of water requirement and fixed Partial Root zone Drying (FPRD) at 100, 80 and 60% of water requirement. Water requirement was determined based on compensation of soil moisture deficit using an electromagnetic moisture meter. Water was measured by volume meters and distributed in the field. The first stress was applied at the 6-leaf stage of maize. Two weeks after applying the first deficit irrigation treatment in the 10-leaf stage of the plants, the first Root sampling performed. Dry weight and volume, lateral and deep penetration of Roots were measured at each sampling. The results showed that in all treatments the average amount of all measured traits decreased with decreasing water consumption. There was no significant difference among Root dry weight of FI, PRD100 and PRD80 treatments. Root volume was affected by water stress but application of PRD80 method prevented the negative effects of water stress on Root volume. Therefore, PRD method is more efficient compared to DI and FPRD methods when applied water stress, and water and nutrients will be absorbed at a higher level by Root.