20
The soils for farms #11 and #12 are not typical for the Chicago Milkshed
area but are coarse sandy soils included in the selection because of their
very low calcium level, These two soils show the lowest 1955 level and the
lowest two year increase in available strontium-90,
While it is possible that
they received less fallout, it is more likely that something in the chemistry
of these two soils acts to reduce the fraction of "available" strontium-90,.
That these soils may be anomalous is further indicated by the unexpectedly low
concentration of strontium-90 in the alfalfa grown on them (see Table 5 and
discussion on page 22 below),
The strontium-90 measurements for the twelve Chicago Milkshed soils collected in late September 1953 have been summarized and discussed elsewhere.>
The
1953 soils show an average of about 50 percent of the total available strontium-90
in the top one inch laver for unplowed soils,
The 1955 soils show about 80 per-
cent of the total available strontium-90 in the top two inches of unplowed soils,
Since this observation applies equally well to the soils showing the lowest
total available strontium-90 (farms #11 and #12), it appears that the leaching
of strontium-90 to greater depths by natural processes is very slow.
«1955 Chicago Milkshed Alfalfas
Results for the alfalfa samples are presented in Table 5 together with the
results for the soils from which they were collected.
The soils are listed in
order of decreasinr concentration of available calcium in the 0-2" depth sur-
face layer, as shown_in colum 2, .
The soil levels of available strontium-90 in "Sunshine Units" are listed
in the third column together with the depth of the soil sample assayed,
The
results for soil samples of 0-2" depth increase fairly regularly with decreasing calcium concentration.
For the three recently plowed soils, the "Sunshine
Unit" values of 0-2" depth are undoubtedly some 2 to 3 times the values given,