Effects of regulated deficit irrigation(RDI) and alternate partial root zone drying(APRI) on grapevine growth and development

Grapes are among the earliest domesticated fruit species and the most economically important fruit crop worldwide nowadays. According to Food & Agriculture Organization(FAO), viticultural area in China had reached 1.96 million acres in 2014. As a perennial deciduous fruit tree, grapevine is quite sensitive to water. Therefore, developing efficient water management strategies that are suitable for our unique climate in China is significantly important; and it has been the focus of massive researches due to increasing water shortage, climate change and global warming worldwide. The aim of this review is to help growers setting up a practical irrigation program that can inhibit vegetative growth of the grapevine, facilitate root development, improve fruit quality, maintain or even enhance yield, reserve nutrition, and ensure winter hardiness. This review summarized two irrigation programs under drip irrigation-regulated deficit irrigation(RDI) and alternate partial root zone irrigation(APRI), from following aspects: 1, the time point when the two programs should be applied on the vines and to what extent the water deficit is appropriate.2, how the two programs influence the soil water content, soil structure, and root systems. 3, how the twoprograms influence the growth and development of grapevine including shoot growth, leaf area index and photosynthesis; and how they influence fruit yield and quality. 4, the two irrigation programs are relatively new and their applications in commercial vineyards in China haven't been well-established. It is necessary to list the precautions to avoid production loss or quality decline. The timing point for DRI is critical.To maintain the yield of table grape, the water deficit should be applied before fruit set; it should be irrigated fully during flowering and berry enlarging periods. But for wine grapes, deficit could be applied during veraison. The degree of deficit is important as well. Conventionally, midday leaf water potential is used in determining water needs. During non-deficit irrigation, full irrigation should be applied when the midday leaf water potential drops below-1.0 MPa. While, during RDI, the leaf water potential should be maintained between-1.2 and-1.4 MPa in order to avoid detrimental influences on the fruit quality and yield. There were not enough studies on the influences of RDI on root development which should be paid more attention in further studies. Proper application of RDI can improve fruit quality. When applying RDI in a commercial vineyard, it is necessary to make sure that the soil samples can reasonably represent the whole area. The optimum dripper distance is about 50-60 cm. All in all, there are three key elements in practical application of RDI: the timing, duration and degree of deficit. For APRI, the timing is relatively flexible but the interval is quite critical. Studies show that the interval can be 10-14 days in temperate climate areas while 7 days in hot climate areas. Take transpiration rate and soil texture into consideration first. Drip irrigation combined with APRI can increase soil permeability, facilitate root development, decrease evaporation between plants and thus increase water-use efficiency. Similar to DRI, APRI also has a significant effect on improving the fruit quality while maintaining yield. Experiments must be taken to confirm suitable interval and irrigation amount before applying APRI in a commercial vineyard. Both DRI and APRI can save irrigation and reduce summer pruning. The differences are: DRI apply water deficit on vines while APRI apply water deficit on soil; the timing of DRI is critical while that of ARPI is flexible;DRI improves quality while APRI has the potential to improve quality via reducing vigor. Compared to RDI, APRI is easier to implement and less risky for growers as yield can be maintained; therefore, APRI should be a priority of further study and application. From abundant studies we can draw a conclusion that both RDI and APRI are better than regular drip irrigation. Compare to RDI, APRI is more practical, less risky and hence is recommended. However, most researches regarding photosynthesis and water-use efficiency are based on single leaf level and a relatively short period of time; but in terms of agricultural irrigation, studies based on a population level over several years are more statistically meaningful to guide large-scale production. Besides, irrigation management is also critically influenced by several factors such as climate, soil condition and plant physiology; these factors are all connected to each other and have complicated relationships. So, further studies should take these factors into concern when developing water regulation techniques, including water permeability and lower limit. In conclusion, water-saving irrigation programs and the timing and deficit degree of RDI can be feasible and optimized for specific local regions. Besides, water-saving irrigation programs and management systems can be developed with combined efforts from computer science and engineering, so that theories and practices can be integrated to the best.