Effect of irrigation and crop load management on fruit nutrition and quality for ambrosia/M.9 apple.

Neilsen, D., Neilsen, G.H., Herbert, L.C., and Guak, S. (2010). "Effect of irrigation and crop load management on fruit nutrition and quality for ambrosia/M.9 apple.", Acta Horticulturae (ISHS), 868, pp. 63-72.

Abstract

Effects of restricting soil moisture and imposing high crop loads on fruit nutrition and quality were examined for Ambrosia/M.9 apple (Malus × domestica) trees planted in 2003 on a sandy loam soil. Each tree received drip irrigation daily from two 4 L.h-1 emitters, located at 30 cm perpendicular to the row. In 2006, four irrigation treatments were randomized to the main plot units: 100% ET (evapotranspiration) replacement; 50% ET replacement; 50% ET replacement to one side of the tree and 50% ET replacement every second day. In 2007, the same irrigation treatments were applied with the one-sided treatment switched to the opposite side. Three levels of reproductive effort (crop load) were established in the sub-plot units including 2.5 (low), 5 (standard) and 10 (high) fruit per cm2 trunk cross sectional area (TCSA). A range of soil moisture levels was established in response to irrigation treatments, although several large rainfall events compromised the deficit irrigation treatments. In 2007, deficit irrigation and crop load both increased plant water stress. Irrigation deficits reduced fruit size up to 16% but did not affect yield or fruit quality in Ambrosia/M.9 apple trees. A 50% ET water deficit was less detrimental if applied more frequently (daily rather than every two days). Fruit size decreased, but yield increased as crop load increased. Under sufficient irrigation, crop loads up to 7.2 fruit/cm2 TCSA would supply fruit with average size 210 g. With 50% ET deficit irrigation, crop loads should likely be adjusted to between 5.7 and 6.8 fruit/cm2 TCSA depending on irrigation frequency. Fruit Ca concentrations were below deficiency levels for all treatments except for the smaller fruit found under high crop loads. As crop load increased, fruit concentration and total tree partitioning to fruit of N, P, K, Mg, B, and leaf concentrations of K and P decreased, suggesting some limitations in availability at high demand. Deficit irrigation reduced fruit Mg concentration, leaf P concentration, and Mg, P and K uptake into individual fruit, indicating either reduced root volume for nutrient uptake or reduced nutrient mobility.

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