other hand, is likely to be more lasting. Soil application is safer than 
spray for plants, such as azaleas, which have delicate tissues that canbe 
easily damaged by the spray. In experimental work thus far, a few plants 
have indicated inability te absorb and utilize a soil-applied chelated metal. 
Effectiveness. The first signs of plant response to a chelated metal 
treatment are the improved greening of developing leaves, and perhaps an 
increase in bud development. When treated plants are in the active grow- 
ing stage, such signs generally appear within a week or two. Benefit from 
a Single treatment may continue for as brief a time as a month or as long 
as several years, depending on the soil-plant situation. 
SOME RESEARCH ADVANCES 
The ARS is among public and private agencies making efforts to learn 
more about the role of chelates in plant nutrition and to develop ways of 
using them to advantage. Following are examples of work conducted by 
ARS scientists alone or in cooperation with a State agricultural experiment 
station or with support of another Federal agency. 
Radioactive Isotope Studies 
Atomic techniques--used in place of the ponderous work of analyzing 
plant tissues--are providing much clear and direct information on nutri- 
tional difficulties that bring about plant chlorosis, and on the effects of 
chelating treatments. In such experiments, a selected isotope--radio- 
active iron, for example--is applied to the soil of a potted plant. The 
extent to which the radioiron is taken up by the plant can be learned by 
placing an X-ray film over the plant in the dark.Radio-emanations expose 
the film, and the higher the concentration of the tagged iron in any part of 
the plant, the lighter the image will appear in the autoradiograph. A faint 
image means that little of the iron is present, and here the plant is chlor- 
otic. 
A number of greenhouse studies at the Agricultural Research Center 
with support from the Atomic Energy Commission have dealt with effects 
of iron,with and without chelate aid, on plants grown in calcareous soils. 
A variety of soybean that is highly susceptible to chlorosis in calcareous 
soils has been used as a test plant in much of this work. The isotope used 
has been sometimes radioactive iron and sometimes a chelate tagged with 
radioactive carbon. 
An autoradiograph of a soybean plant that took upradioiron effectively 
by aid of a chelate is shown in Figure 2. The evenly pronounced image 
indicated that ample radioactive iron reached all parts of the plant. 
Without a chelate, the same soybean plant variety grown in the same 
soil got almost no benefit from a radioiron supplement. The tagged iron 
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