ISHS Acta Horticulturae 57: I International Symposium on Tropical and Subtropical Fruits
THE USE AND IMPORTANCE OF CHELATING AGENTS IN THE NUTRITION OF TROPICAL AND SUBTROPICAL FRUIT SPECIES |
| Author: | A. Wallace |
| Abstract:
Many tropical and subtropical fruit species are subject to Fe chlorosis, especially when grown on calcareous desert soils which have been reclaimed for irrigated agriculture. Susceptible species to such Fe deficiency include avocado, mango, macadamia, cacao, banana, pecan, coffee, tung, and others. Some fruit and berry species become Fe-chlorotic on noncalcareous soils because of soil conditions and/or genetic characteristics of the trees. Iron chelates are very useful in the correction of Fe chlorosis under many conditions for many species. High cost is a deterrent under some conditions; however, chemical industries continue the search for new chelating agents for agricultural use. One new Fe chelate has given phenomenal response to deciduous fruit trees in Spain when applied at rates of 50 and 100 g per mature tree per year. Zinc chelates also have uses in fruit tree production. Avocados planted on hillsides in California are best fertilized with Zn chelate when necessary because it is the easiest procedure to use. Zinc chelates are often mixed with liquid fertilizers because it is one means of keeping Zn in solution in such fertilizers. Rootstocks or scions which have resistance to micronutrient deficiencies would decrease the need for metal chelates. Physiological factors associated with resistance to Fe deficiency are the excretion of H+ by plant roots and reduction by root surfaces of Fe+++ to Fe++. Synthetic chelating agents have been used since 1952 in the correction of Fe deficiencies in susceptible crops (Stewart, 1963; Wallace, 1962, 1971), and since about 1960 for application of Zn to crops under some special conditions (Wallace, 1962, 1971; Wallihan et al., 1958). Both uses have limitations, but when properly used they can be very beneficial (Wallace, 1966). Chelate use in plant nutrition has been the subject of many literature reviews (Brown et al., 1962; Norvell, 1972; Stewart, 1963; Wallace, 1962, 1963, 1965, 1966, 1971). The following 34 points generally summarize the present status of metal chelates in plant nutrition, including tropical and subtropical fruit species, plus some of the problems associated with their use:
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