The effects of irrigation at different soil water levels on the water use characteristics of apple trees

SummaryIn a medium-long term project with Granny Smith apple trees irrigations were applied at four soil water (TAW) levels, 85%, 65%, 45% and 25%, to replenish soil water to differentiated water extraction depths. The latter were divided into three or four layers from 700 mm to 1100 mm, depending on the rooting depth and the treatment. The treatments were applied in each of four phenological phases of the trees. The maintenance of a seasonal 85% TAW level required 983 mm of irrigation water, compared to 272 mm for a 25% TAW level. During the peak growing period an 85% TAW level needed an irrigation every 5.9 days and a 25% TAW level every 54.7 days. During this period the 85% and 25% TAW levels caused actual evapotranspiration (ETa) rates of 9.5 and 3.1 mm d−1, respectively. The ETa/E0 (pan evaporation) ratios during the same period were 1.63 and 0.51, respectively, for an 85% and a 25% TAW level. Trunk, shoot and fruit growth were found to be positively correlated with an increase in the TAW levels during specific growth phases. Quality parameters such as fruit size distribution, bitterpit, watercore and superficial scald also showed marked interaction with the treatments. The optimum sequence of TAW levels (%) were found to be 25/45/85/25 for the four phases. This sequence yielded an ETa of 1 099 mm and a seasonal ETa/Eo ratio of 1.01.