Effect of the number of drippers and irrigation frequency on production, fruit quality and water productivity in a high-density apple orchard

]Field experiments were conducted during three consecutive years to determine the effect of the number of drippers per plant and irrigation frequency on the production, quality and water productivity parameters in ten year old apple trees, cv 'Golden Delicious' on rootstock EM9, grown in an intensive system with high-density planting in an alluvial soil of north-eastern Spain. The experiment consisted in applying the same dose of water, determined according the irrigation water needs, through three different agronomic designs (1, 2 and 3 8 Lh-1 pressure-compensating drippers per tree), maintaining a constant irrigation time and varying the irrigation frequency (3, 6 and 9 days on average). No differences were observed among the three treatments for any of the variables analyzed (P<0.05), except for starch index. The lack of differences in production parameters between treatments, can probably be attributed in part to the standardization of the hydric pattern eventually developed in the three designs, due to the same water amount of water applied and also because the formation of a strip of continuous moisture along the crop row caused by the proximity between drippers. In the test conditions, the agronomic design with 1 dripper per tree and 3 days frequency achieved similar yields to those obtained with 2 or 3 drippers and lower irrigation frequencies, thus reducing installation costs.