Iron in citrus production

Twenty-three navel orange trees were grown in outdoor solution cultures for a period of 11 years to measure the effect of iron deficiency on fruit production and quality. When the concentration of iron in spring-cycle leaves was below 30 ppm (based on weight of dry leaves) in September, the production of fruit was less than when iron concentration exceeded 30 ppm. As the iron content decreased below this value, fruit production declined progressively and reached essentially zero at 15 ppm of iron. Fruit quality at harvest was not seriously affected except for some loss in color and the fact that iron content of the juice was about proportional to that in the leaves. The decrease in yield was due to fewer fruits being matured. Actual fruit sizes were the same or slightly larger in iron-deficient trees. Twig dieback was observed as a symptom of the degree of iron deficit that caused loss of fruit yield.