Stomata are essential to the plant because in addition to controlling water loss from leaves they provide the principal route for the uptake of carbon dioxide from the atmosphere. On the one hand, stomata have to remain sufficiently open to provide a pathway for the uptake of carbon dioxide to satisfy demands from the developing crop and vegetative growth and, on the other, they must prevent excessive water loss through a reduction in aperture. These counterpoised priorities have led to the evolution of complex and sophisticated control mechanisms which take their signs from variables such as light, atmospheric carbon dioxide, temperature and soil water availability. The only one of these variables over which we have any degree of control is the latter: soil water availability. The Partial Root Drying (PRD), a innovative irrigation system, began in about 1992 in CSIRO – Australia and in other laboratories around the world, showed that if part of the root system was slowly dried and the remaining root kept well watered, abscisic acid (ABA) produced in the drying roots reduced stomatal aperture. At the same time the fully hydrated roots maintained a favorable water status throughout the aerial parts of the plant. In other words, it was possible to separate the biochemical response to water stress from the physical effects of reduced water availability. Aiming at testing how the PRD affected the WUE in potato crops a series of experiments were conducted in a desert area in Lima Peru at the International Potato Center. The PRD was compared with Conventional Irrigation (CI) on an early vegetative cultivars (4 months) grown in randomized plots with furrows. Plants were irrigated normally for 42 d, stage at which the corresponding treatments were applied. The PRD system consisted of alternately irrigating one of the two neighboring furrows during consecutive watering. CI was the conventional way where every furrow was irrigated during each watering. PRD and CI were further divided into two treatments with different watering amounts resulting in total 4 irrigation treatments, two of CI with 100% of the water typically applied to the crop in Lima (CI) and 50% (CI1/2) of the water laminae according with crop requirements. The PRD1 treatment received the same amount of water as CI1/2 and the PRD1/2 received half of the water applied to PRD1. Fresh tuber yield was higher for CI (43.1 t.ha-1), followed by PRD1 (33.4 t.ha-1), CI1/2 (30.0 t.ha-1) and PRD1/2 (27.4 t.ha-1). WUE was higher for CI1/2 (74.9 kg DM.ha-1. mm-3) followed by PRD1 (58.3 kg DM.ha-1. mm-3), CI1/2 (51.3 kg DM.ha-1. mm-3), and CI (43.9 kg DM.ha-1. mm-3). This irrigation system might become an alternative to large areas in the world producing potato, where water is limiting and where salinity might become a problem.