Long chemical names of chelates are frequently abbreviated for con- 
venience. Here are abbreviations and full names of four of the chelates 
used in ARS experiments: 
EDTA -- Ethylenediamine tetraacetic acid 
HEEDTA -- Hydroxyethyl ethylene diaminetriacetic acid 
DTPA -- Diethylene triamine pentaacetic acid 
EDDHA -- Ethylene diamine di(o-hydroxyphenol acetic acid) 
Of these four, EDTA and HEEDTA are most effective in making iron 
and zine available to plants in acid and slightly alkaline soils. DTPA and 
EDDHA are more effective than EDTA and HEEDTA in calcareous soils. 
EDDHA is not currently on the market. 
Evaluating a Chelating Treatment 
In plant research, whether a chelated metal treatment is found prac- 
tical and advantageous depends on a combined evaluation of answers to 
these questions: 
4% 
What yield increase or other benefit does a plant show after treat- 
ment? 
How long is one treatment helpful ? 
Does the treatment damage the plant by toxicity? 
What does the treatment cost? (A relatively expensive treatment 
may be economical if one application is sufficiently effective and 
lasting. ) 
%* + * 
Some General Findings 
Since chelate treatments are tailored to suit specific soil-plant situa- 
tions, the following general statements are not directions for use, but will 
give some idea of current ranges of practical applications and results to 
expect. 
Strength. Application of a small amount of chelated metal is the in- 
variable rule for plant safety and economy. Overdosages can be toxic to 
plants and the margin of safety is sometimes small. 
Spray solutions are likely to be made with 1 to 5 pounds of chelated 
metal in 100 gallons of water. Soil applications for trees range from a 
few ounces to as much as 8 pounds of chelated metal around each tree; 
field applications, 20 to 400 pounds per acre, depending on the plant and 
the chelate employed. For ornamentals, a teaspoon of chelated metal per 
plant is often enough. 
Soil application vs. spray. Chelated metal in a spray is likely to be 
cheaper and easier to apply than a soil treatment. Soil application, on the 
see 
