Evapotranspiration-based Irrigation Systems and Nitrogen Effects on Yield and Fruit Quality at Harvest in Fully Mature ‘Fuji’ Apple Trees over Four Years

In a long-term study between 2008 and 2011, the use of crop evapotranspiration (ETc), when a precise crop coefficient value ( K c ) was used, provided a reliable irrigation scheduling for determination of water requirement for ‘Autumn Rose Fuji’ apple ( Malus × domestica Borkh) fully mature trees. Water use, yield, and fruit quality attributes at harvest were examined under various irrigation and nitrogen (N) systems that were scheduled using ETc. Trees with a full sprinkler (FS) system received ≈39% to 41% more water than those with a full drip (FD) system during the period of 2008–11 growing seasons. On average, mature trees with an FS system received 5927.6 L (944 mm), whereas those with an FD system received 3610.3 L of water per tree (554.9 mm) per growing season over the period of 2008 through 2011. Fruit from trees with FS and FD were larger, whereas those with 50% FS were smaller than those from all other treatments. Trees with 50% FS treatment received a higher volume of water but had smaller fruit size than those with 50% FD or 65% FD. Averaging values over 4 years revealed that applications of any form of deficit irrigation (DI), either by microjet irrigation or drip, increased fruit soluble solids concentration (SSC) and firmness but decreased water core at harvest. Considering yield, and quality attributes in this study, a well-calculated ETc-based FD irrigation system is recommended over any other irrigation regime. If application of deficit water is mandated, application of 65% FD is preferred over 50% FS, as trees with 65% FD treatment received less water while had larger fruit than those of 50% FS. Trees receiving 80 g N/tree had lower fruit color and russet than those receiving 40 g N/tree. However, other yield and quality attributes were unaffected by the rate of N fertigation.