Iron Deficiency of Apple Tree as Affected by Increasing Soil Available Phosphorous

Abstract

ABSTRACT Chlorosis induced by excessive phosphorus (P) fertilizer application is a common problem in many apple orchards in Iran. This experiment was conducted to study the relationship between P, zinc (Zn), and iron (Fe) in apple trees. Young ‘Delicious’ apple trees were planted in the pots, in which the soil P was added at rates of 0, 1500, and 3000 μ g P (as diammonium phosphate) per g of soil. In the second year, when trees were established and leaf chlorosis appeared, a commercial Fe-EDDHA chelate applied at two rates of 0 and 9.5 μ g Fe per g of soil. Results showed that adding P to the soil increased soil available P and Zn. Increasing soil available P up to 4 times of recommended ranges, had no negative effect on leaf chlorophyll index, leaf surface area, or dry weight of young and old leaf and root dry weight. Young leaf and root P concentrations and total leaf dry weight increased as soil available P increased. Increasing soil P level caused no Fe or other nutrient accumulation in roots. Iron chelate applications corrected chlorosis and increased Fe concentration in young and old leaves, but decreased manganese (Mn) concentration of roots. These changes were not affected by increasing soil P levels. Iron chelate declined root Zn in control treatment, but as the soil extractable Zn increased by applying P to the soil, no changes in Zn concentration was observed. Based on this experiment, it seems that ‘Delicious’ apple is not sensitive to high available P in the soil.