1. Summary In this study we report the partial root-zone drying (PRD) irrigation technology with 50% and 25% irrigation water compared to flood irrigation applied to the potato in the shelter and open field in three different sites in North China. PRD has been successfully used in crops such as tomatoes, grapes, oranges, olive trees, maize, and cotton in which it reduced the consumption of water by more than 50% without negative effects on yields. Research on the use of PRD in root and tuber crops has been conducted, particularly in semi-arid environments. However, issues such as at which growth stage and how much water to use in PRD should be applied to the potato crop to improve WUE without yield reductions remain to be addressed. Therefore, we assumed that PRD irrigation method with half or less than half of water used in flood irrigation will be suitable for potato production in areas with limited water resources in China. Introduction PRD (Figure 1) is an irrigation technique whereby half of the root zone is irrigated while the other half is allowed to dry out. Water supply is then cyclically reversed allowing the previously well-watered side of the root system to dry down while fully irrigating the previously dried. The PRD technique in potato has allowed significant reductions of water (40-50%) with increased water use efficiency (WUE) and without tuber yield reduction. One challenging aspect is to find the appropriate water restriction in timing, duration and intensity of the water restriction in potato that could lead to some tolerance traits without affecting tuber growth. The purposes of the present work is to find the right amount of irrigation water of PRD for potato with increasing WUE but no significant reduction in tuber yield, and initiation timing for water restriction treatments by investigating the timing of tuber initiation onset in arid area in North China. Materials and Methods The experiments were conducted in Hohhot and Lanzhou in the open field in 2011 and Zhangjiakou both in shelter and open field in 2013. The treatments were FI(flood irrigation), FI 50, PRD 50, PRD 25, RF(rainfed) in 2011, FI 100, E-PRD 50, L-PRD 50, E-DI 50 (drip irrigation), L-DI 50 in 2013. 50 and 25 refer to 50% and 25% of irrigation water used compared to FI treatment. E and L refer to first irrigation right after tuber initiation and two weeks after tuber initiation. Results In 2011, PRD 50 treatments produced 30.0t/hm 2 and 15.7kg/hm 2 yield respectively which had no significant effect compared with FI treatments which produced 32.9t/hm 2 and 15.6kg/hm 2 in Hohhot and Lanzhou(Figure 3A,3B). In 2013, the yield of all the treatments had no significant differences both in shelter and open field in Zhangjiakou(Figure 3A,3B). Figure 2. Three different irrigation techniques Figure 1. Comparing PRD with Conventional irrigation(Flood irrigation) Figure 3. Yield of different treatment in different sites Conclusions PRDs treatments with less water produced higher WUE and non- significant reduced yield compared with FIs treatments in the typical arid area in North China which may the potential technology for irrigated areas in Asia under SO2. There were no significant differences in yield among DI and PRDs treatments, which highlights that PRD allows to save not only water but also at the same time money. Bibliography Gu, S., Du, G., Zoldoske, D., Hakim, A., Cochran, R., Fugelsang, K., Jorgensen, G., 2004. Effects of irrigation amount on water relations, vegetative growth, yield and fruit composition of Sauvignon blanc grapevines under partial rootzone drying and conventional irrigation in the San Joaquin Valley of California, USA. J. Hort.Sci. Biotechnol. 79 (1), 26–33. Sadras, V.O., 2009. Does partial root-zone drying improve irrigation water productivity in the field? A meta-analysis. Irrig. Sci. 27, 183–190. Kaiyun Xie 1 Junhong Qin 1 Ramirez David 2 1 CIP-China Center for Asia Pacific, International Potato Center, 709 Pan Pacific Plaza A12 Zhongguancun Nandajie, Beijing, China 2 Applied Biotechnology Laboratory, International Potato Center, P.O. Box 1558, Lima 12, Peru Enhancing potato yield per drop of supplementary water Partial Root-zone Drying Irrigation Conventional irrigation Partial root-zone drying Treatment in the shelter in Zhangjiakou Table 1. The irrigation water amount and rainfall in each experimental site FI PRD DI Treatment in the shelter in Zhangjiakou Figure 4. WUE of different treatment in different sites In 2011, rainfed treatments produced the significantly highest WUE, FI produced the significantly lowest WUE compared with other treatments in Hohhot and Lanzhou(Figure 4A,4B). In 2013, L-PRD 50 treatment with 7.0kg/m 3 WUE was significantly higher than the others except E-DI 50 and L-DI 50 but not significantly in the shelter(Figure 4C). Although WUE of all the treatments had no significant differences, FI was the lowest in open field(Figure 4D). A B CD A B CD