1. Partial Root Drying: an Alternative Irrigation Management to Improve the Water Use Efficiency of Potato Crops Adolfo Posadas 1,2,*, Roberto Quiroz 1, Guliver Rojas 1,3, Miguel Málaga 1,3 1 Centro Internacional de la Papa, Apartado Postal 1558, Lima 12-Perú, 2 Facultad de Ciencias Físicas, DAFI, UNMSM, Lima 1, Perú 3 Escuela de Post Grado, UNALM, Lima 12, Peru *Corresponding Author: a.posadas@cgiar.orga.posadas@cgiar.org 1. Introduction Partial Root Drying (PRD) is a innovative irrigation system, initiated at CSIRO, Australia and in other laboratories around the world in the early 90’s. Scientists showed that if part of the root system was slowly dried and the remaining root kept well watered, abscisic acid (ABA) was produced by the drying roots thus reducing 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. Although PRD was successfully implemented in tomatoes, grape, and oranges, there is no research in root and tuber crops, particularly for arid and semi-arid environments where the water resource is scarce. 2. Methods The PRD irrigation might become an interesting alternative for potato cropping in arid and semi-arid environments. These conditions are ubiquitously distributed around the world. Augmenting the water use efficiency will require diminishing the adaptation period to just the time required for establishing the root system. This have to be researched for the different varieties cropped around the world. Nonetheless, even under the conditions of the present experiments the savings in the amount of water used was substantial, precisely when the irrigation water is scarce. 4. Conclusion 5. References 1.- Levitt J. 1972. Responses of plants to environmental stresses. Ed. Academic Press. New York. 667 p. 2.- Bacon, M.A. 2003. Partial Root Drying: A sustainable irrigation system for efficient water use without reducing fruit yield. The Lancaster Environmental Center, Lancaster University. http://www.lancs.ac.uk/dpts/psihttp://www.lancs.ac.uk/dpts/psi 3.- Hsiao, T. C. 1973. Plant responses to water stress. Ann. Rev. Plant Physiology 24: 519 – 570. 4.- Wilkinson S. & Davies W. J. (2002) ABA-based chemical signalling: the co-ordination of responses to stress in plants. Plant, Cell and Environment 25(2), 195–210. 5.- Loveys, B.R., Grant, W.J.R., Dry, P.R. and McCarthy, M.G. (1997) Progress in the development of partial root-zone drying. Australian Grapegrower & Winemaker 403:18-20. 6.- Horton, D. & Sawyer, R.L. 1985. The potato as a world food crop, with special reference to developing area. In: Potato Physiology. Li Paul, H. (ed.). Academic Press Inc. Ltd., (London), UK. Pages 1-34. Table 1. Yield in Tn/ha A series of experiments with potato var. Unica, were conducted in a desert area in Lima Peru at the International Potato Center, where the average rainfall is 23 mm.y -1. Soils were sandy loams with good drainage. A complete randomized block design with 5 replicates was used to compare four watering treatments (See Figure 1). The distance among plants was 0.30 m. and among furrows, 0.9 m. The conventional furrow irrigation scheme was used. The water was siphoned into the furrows from the irrigation canals (See Figure 2) to measure the amount of water per day-furrow. In the case of the PRD treatments, the furrows with irrigation were alternated each week. All plants were irrigated normally for 42 d, stage at which the corresponding treatments were applied.. Figure 2. Experimental unit and water siphons Establishing the crop for 42 d consumed 2720 m 3 of water per ha. The total consumption of water per treatment were: 4760, 3740, 3740, and 3230 m 3 per ha for CI 1, CI 2, PRD 1, and PRD 2, respectively. Fresh tuber yield was higher for CI 1 (43.1 t.ha -1 ), followed by PRD 1 (33.4 t.ha -1 ), CI 2 (30.0 t.ha -1 ) and PRD 2 (27.4 t.ha -1 ). WUE was higher for CI 2 (74.9 kg DM.ha - 1. mm -3 ) followed by PRD 1 (58.3 kg DM.ha -1. mm -3 ), CI 2 (51.3 kg DM.ha -1. mm -3 ), and CI 1 (43.9 kg DM.ha -1. mm -3 ). The dry matter content was higher (P<0.05) for the PRD 2, a characteristic desirable for the Andean consumer. The water use efficiency gain with the PRD was low compared to the reports in other crops (e.g. tomato, a solanaceous crop). This difference was due to the 42 d with full irrigation compared to the experiments in tomatoes where the PRD treatment was initiated after 7 days, once the root system was established. Type of Treatments Tn/ha Commercial Tubers Tn/ha Non- Commercial Tubers Total Tn/ha Fresh Tub % Commercial Tub T143.121.0044.1297.74 A T2 29.990.9030.90 97.11 A T3 33.431.39 34.82 96.10 A T427.43 1.14 28.57 95.84 A 3. Results and Discussions Water use and yields in potato with control irrigation (CI 1, CI 2 ) and PRD (1, 2) 0 20 40 60 80 100 120 CI 1 CI 2 PRD 1 PRD 2 Type of Irrigation Tn - m 3 /ha Total Yield (ton/ha) Comercial Potato (ton/ha) Percentage Irrigation (%) Watering treatments T1:100 % amount of irrigation (CI 1 ) T2: 50 % amount of irrigation (CI 2 ) T3:100 % amount of irrigation (PRD 1 ) T4: 50 % amount of irrigation (PRD 2 ) Figure 1. PRD methodology and treatments First irrigationSecond irrigation Wet zoneDry zone First irrigation: furrow 2 and 4 Second irrigation: furrow 1 and 3 First irrigation: furrow 1, 2, 3 and 4 Second irrigation: furrow 1,2, 3 and 4 YIELDS OF FRESH AND DRY TUBER per m 3 OF APPLIED H2OH2O 12.09 12.14 12.58 12.90 2.7 2.9 3.3 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 CI 1 CI 2 PRD 1 PRD 2 Kgs Kgs fresh tuber per m 3 H 2 OKgs dry tuber per m 3 H 2 O