produced a faint image of roots and lower stems on an autoradiograph, and 
practically no image of foliage. This indicated that the supplemental iron 
did not remain available for plant growth but was changed in the soil to an 
unavailable form. 
Different chelates and different rates of treatment have been used in 
the isotope studies of test plants. The outward appearance of plants and 
corresponding inner signs have been observed when increasing amounts of 
a chelate-and-iron treatmert improved the greening of plants up to the 
point where overdosage produced toxic symptoms. The variable effect of 
the nature of the soil has been shown by applying the same chelate-and- 
iron treatment to a number of different calcareous soils. The same treat- 
ment, which alleviated chlorosis in the test plant in some soils, was less 
effective in other soils, and caused the plant to show toxic damage in still 
other soils. 
Wheatland milo used in isotope experiments has given evidence that a 
plant species may be unable to utilize chelated iron. This variety of milo 
was found to be susceptible to iron chlorosis in two calcareous soils. 
When a treatment of radioactive iron chelated with DTPA was tried for 
these plants, they did not improve appreciably in above-ground growth. 
Dark autoradiographs eXplained the failure of the Wheatland milo plants to 
improve: they did not absorb and transport worth-while amounts of the 
chelate-protected iron. 
Chelated Metal Treatments for Crops 
Pears. A practical chelated metal spray treatment has been devel- 
oped which improves the greening and fruit yields of iron-chlorotic pear 
trees grown on clay adobe soils of the Rogue River Valley in Oregon. This 
work has been done cooperatively by scientists of the Oregon Agricultural 
Experiment Station and the ARS. 
Pear growers in this area have fought chlorosis in the past by inject- 
ing iron citrate into trees. The practice was time-consuming and trees 
showed damage after repeated injections. 
In the chelate experiments, 1,500 pear trees were given various che- 
lated metal treatments over several years. The greatest benefit to the 
trees without toxic damage was obtained with a spray containing the chelate 
DTPA compounded with both iron and manganese. The role of the man- 
ganese is not clearly understood. Nevertheless, with manganese added to 
the iron the amount of chelate itself could be doubled without toxic effect 
and, therefore, one treatment could do the work of two. The spray rec- 
ommended contains 1 pound of iron-DTPA and 1 pound of manganese-DTPA 
to 100 gallons of water, applied at the rate of 300 gallons per acre. The 
spray gives best results when applied in the first half of the growing sea- 
son: first treatment when spur leaves are three-fourths grown; the sec- 
ond, about 2 weeks later. Two are likely to be sufficient, although severely 
ee 
