a. Experiments on uptake through roots.—it has been fairly clearly established that the
uptake of Sr by plant roots is controlled predominantly by the quantity of available Ca in the
soil: Sr and Ca behave nearly like isotopes of the same element.
Menzel, of the U. S. Department of Agriculture, grew cowpeas on 42 American soils to which
equal amounts of bomb debris had been added. Available Ca in these soils ranged from 0.7 to
48 milliequivalents Ca/100 gm soil. The Sr-90/Ca ratio of the plants was approximately inversely proportional to the available Ca in the soil over the full range of calcium availability.
In another set of experiments on a particular type of soil (Evesboro) to which known amounts
of Sr-89 had been added at two carrier levels, the results listed in Table 2 were found. Thedistribution factor Ks,, defined as (Sr/Ca) pint/(Sr/Ca).ou, Indicates the discrimination which the
plant makes between Sr and Ca uptake.
Crop
(Sr/Ca) soil
ker
|
Lu aA
=~ me
ee: ay . ee ‘ ~f
¢
TABLE 2
kpa
tt faemammin|
Buckwheat... JOO ccs creece) OAR 0088
Cowpens... faa 53
|
0.087
By combining these two sets of experiments, Menzel concluded that average uptake of Sr
from the 42 American soils was best fit by a distribution factor of kg,—0.36.
Comparisons of Sr and Ca competition have been made for root uptake from nutrient solutions.
Under these conditions, Menzel found a distribution factor of 1, in agreement with the
published data of Collander.'"* Further experiments on the stable Sr content of plants and
soil under natural conditions are in progress to clarify the picture of comparative Sr and Ca
uptake.
When Sr is not distributed uniformly throughout depth of soil, uptake depends on root
depth. Menzel has compared the feeding of year old alfalfa and Kentucky bluegrass on Ca—45
layered at 3 different depths in experimental plots. The results, shown in Table 3, illustrate this
dependence, although depth of feeding varies widely with soil conditions.
TABLE 3
Depth of Cat
o”
Alfalfa uptake
af
12;
2.5 units
5.7
2.8
| Biuegrass uptake
|
|
|
9.3
4.7
0.8
b. Experiments on uptake through the leaves.—Experiments on leaf uptake are underway
at Michigan State College and the University of Arizona. Preliminary experiments at Arizona
have shown that a considerable fraction of Sr placed on leaves as a dilute nitrate solution is
retained. Biddulph has shown that Ca-—45 administered to leaves in solution form can befairly
readily metabolized but is not translocated out of the absorbingleaf.
c. Observations on atomic test debris (Project Sunshine)—Correlated sets of alfalfa and
soil samples from the Chicago milkshed, September, 1953, have been analyzed for Sr—90 content
Footnote references on pp. 42-43.
gaa
|
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ES
TNR ARCHIV