The Impact of Rootstock and Irrigation on Water Use, Tree Growth, Nutrition, Yield, and Fruit Quality of 'Pacific Gala' Apple

Water usage, tree growth, leaf mineral nutrients, yield, and fruit quality attributes in 'Pacific Gala' apple (Malus x domestica Borkh) on four rootstocks: Budagovsky 9 (B.9), Malling 9 (Nic29), Supporter 4, and Geneva (R) 30 (G.30); and two irrigation systems: Full sprinkler (FS), and Full drip, (FD) were studied during 2002 through 2007. Drip irrigation significantly reduced tree water use during all growing seasons, without any adverse effects on fruit quality or yield. Trees used more water in July than any other month. 'Pacific Gala' trees on B.9 had the smallest trunk cross sectional area (TCA), and smaller leaves, and lower leaf potassium (K) than those on other rootstocks. Fruit from trees on B.9 and G. 30 often had better color and more advanced starch degradation pattern (SDP) but had lower firmness as compared to those from other rootstocks. Trees on Supporter 4 were larger and had higher leaf K but lower yield, leaf nitrogen (N) and magnesium (Mg) than those on other rootstocks. Trees on Nic29 often had higher yield per tree and larger fruit size than trees on other rootstocks, particularly in 2004 and 2005. Yields and fruit size from trees receiving drip irrigation were higher than those with sprinkler irrigation during 2004 and 2005, while the differences became less pronounced during the later years. Fruits from drip irrigation were slightly more advanced in maturity as they had higher SDP as compared to trees with sprinkler system. Trees with drip irrigation had lower leaf calcium (Ca), K, and Zn, but higher Mn. In general, Nic29 can be a suitable rootstock and drip irrigation is a preferred method of irrigation for 'Pacific Gala' under conditions of this experiment.