In two field studies with `Redchief Delicious'/MM.106, 'Empire'/M.9/MM.106 and 'Mutsu'/M.9/MM. 106 trees on fertile silt loam soils, trickle irrigation increased vegetative growth during the first three years and resulted in a 16%-20% increase in cumulative yield over the first five years. When fertilizer was injected into the irrigation water weekly from mid-April until the end of June, tree growth was further increased and cumulative yield was improved an additional 11%-15% for a total of 27%-35% greater yield than the non-irrigated trees. In these studies, ground fertilization did not improve growth or yield unless trickle irrigation was also applied. However, ground fertilization was not as effective as fertigation.
Irrigation and fertigation increased the dry weight of roots by 23% and that of shoots by 36% in the first year resulting in a 10% reduction in the root/shoot ratio. Total tree dry weight was increased by 30% if trees were planted early (April 14) but only 14% if trees were planted late (June 10).
Early planting resulted in 17% greater cumulative yield than trees planted late. Initial tree caliper also had a significant effect on early growth and yield with large caliper trees yielding 12% more than the small caliper trees. The interaction of planting date, tree caliper and fertigation resulted in a 50%-70% increase in yield during the first five years.
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