495 Partial Root-Zone Drying (PRD) Feasibility on Potato in a Sub-Humid Climate A. Battilani 1 , C.R. Jensen 2 , F. Liu 2 , F. Plauborg 3 , M.N. Andersen 3 and D. Solimando 1 1 Consorzio di Bonifica di Secondo Grado per il Canale Emiliano Romagnolo, Italy 2 Copenhagen University, Faculty of Life Sciences, Dept. of Agricultural Sciences, Denmark 3 University of Aarhus, Faculty of Science and Technology, Denmark Keywords: deficit irrigation, water use efficiency, Solanum tuberosum Abstract A field experiment was carried out in Northern Italy, within the frame of the EU project SAFIR, to test the feasibility of partial root-zone drying (PRD) irrigation management in potatoes and to compare the PRD irrigation strategy with regulated deficit irrigation (RDI). PRD increased total and first class tuber yield by 4.7% compared to RDI. Tuber weight was significantly (P<0.05) higher in the average as compared with RDI (+14.9 g). In dry years, PRD produced significantly more starch and less reducing sugars than RDI, but this did not occur in the rainy year. Water and Nitrogen Use Efficiency (WUE, NUE) were similar between irrigation treatments. The income for each cubic meter of water or kg of nitrogen was highly variable and not statistically different between PRD and RDI. Crop gross margin per hectare shows a tendency to increase with PRD (average +256 euro ha -1 ), although not steadily and not sufficiently to overcome the higher irrigation system and management costs. INTRODUCTION Agriculture water use is expected to be increasingly limited by ongoing climate change. Moreover, governments worldwide are targeting reduction in agricultural water use. However, water is not only essential for plant growth but also to obtain economically viable production levels and quality. This involves economic and ecological constraints related to unpredictable frequency and severity of droughts leading to limited water access for farmers. Hence, a more efficient use of water resources must be a major focus in coping with the growing water scarcity (Morison, 2008). The first step toward a more efficient use of water is the adoption of novel technologies and irrigation strategies. Improving irrigation management is most likely the best option in most agricultural systems to increase the efficiency of water use (Steduto et al., 2007). One of the most promising management options is regulated deficit irrigation (RDI). As for deficit irrigation, this irrigation strategy aims to restore less than full plant evapotranspiration and have proven to increase the yield per unit of applied irrigation water (Fereres and Soriano, 2007). RDI reduces the risk of adverse effect on yield by imposing water stresses at key stages of vegetation and tuber development, effectively reducing non-productive water use. As less water is supplied, mild soil drying occurs inducing partial stomatal closure reducing transpiration; however photosynthesis is less or only slightly reduced (Jones, 1992) while resulting in a better control of vegetative vigour often bringing augmentation of tuber quantity and/or quality, and as a consequence both irrigation water productivity (IWP) and water use efficiency (WUE) improve (Shahnazari et al., 2007). Partial root-zone drying (PRD) irrigation (Loveys et al., 1999, 2004), can be also successfully applied to potato (Liu et al., 2006; Ahmadi et al., 2010). During PRD, water is distributed only to half of the root system while the remainder is allowed to dry. It is hypothesized that under PRD roots in the dry soil compartment sense soil drying and produce continuously sufficient amount of the root-based chemical signals, mainly abscisic acid (ABA), to induce a physiological response to water stress reducing leaf expansion and stomata conductance. Simultaneously the wet soil part can provide sufficient water to the plants to keep a good water status of the shoot, thus not affecting the general cell turgor (Kang et al., 2004). The wet and dry sides shall be alternated in a Proc. VII th IS on Irrigation of Horticultural Crops Eds.: P. Braun et al. Acta Hort. 1038, ISHS 2014