a 
Irrigation water or other water supplies may have a high content 
of calcium or sodium bicarbonate, which tend to interfere with the 
solubility of iron. 
4% 
Long use of fertilizers or pesticides may build up trouble-making 
deposits of certain minerals ina soil. This has occurred in some 
of Florida's acid, sandy soils long planted to citrus. Several 
years ago, ARS scientists analyzed some of these soils and also 
feeder roots and leaf tissues of iron-chlorotic citrus trees grown 
in the soils. They found that excessive copper prevented the foli- 
age from getting requirements of iron. They have advised that in 
this Situation growers make minimum use of fertilizer and pesti- 
cide sprays containing copper. 
TREATING PLANT CHLOROSIS 
Chelated metals, like other plant nutrient supplements, are tempo- 
rary remedies for controlling deficiencies. Unless the initial cause of the 
deficiency can be corrected, a chelated metal treatment needs to be re- 
newed when effectiveness wanes. 
In developmental work, chelates are frequently compared experi- 
mentally with older treatments for chlorosis, to learn whether a chelated 
metal shows some advantage in effectiveness, economy, or convenience 
over other possible treatments. 
Older Treatments for Chlorosis 
Farmers have fought chlorosis in valuable trees for many years with 
increasing success but not to their entire satisfaction. Few resort any 
longer to the crude process of driving iron nails into ailing fruit trees in 
hope of improving yields. Research long since provided more practical 
treatments, such as iron salts in sprays, injections, and soil applications. 
These old research-based treatments often give reasonably good returns 
and are still the most economic controls for some chloroses. These 
treatments are effective for periods from a few weeks to several years. 
Their repetitive use, especially in large-scale planting, calls for much 
time-consuming labor and the treatments are not helpful to some chlorotic 
plants. 
Some Types of Chelates Employed 
Chelates have already been produced from varied combinations of 
chemicals, and additional formulas with agricultural promise continue to 
be developed. Plant research includes work with some chelates that are 
still in an experimental stage as well as work to extend the usefulness of 
chelates that have been put on the market. 
= Ape 
