704
WARD, JOHNSON, AND STEWART
of the feed were collected daily. The total feed intake and the total milk
production were recorded for each cow.
All samples were analyzed for *’Cs by gamma-ray Spectrometry.
The detecter used was a 4-in.-thick by 8-in.-diameter Nal(Tl) crystal
shielded from background radiation by a 5-in.-thick steel-wall chamber. It was connected to a 400-channel pulse-height analyzer. Rain
elution was counted in 1-liter bottles, and sediment was counted ona
4-in.-diameter filter pad; both were placed directly on the crystal.
Hay and forage samples were counted in 2'-gal cardboard con-
tainers standardized by weight and density to a constant geometry.
Milk samples were counted in a 5.47-liter beaker. Empirically determined spectrum-stripping equations were used to determine the
ICs activity. Crude-fiber determinations were made according to the
standard Association of Official Agricultural Chemists method.
RESULTS
Precipitation-Forage Transfer of 137Cs
It is generally assumed that most of the 371Cs found in forage
plants arises from direct foliar absorption and that soil uptake is
minor.! We have attempted to show soil uptake of fallout "Cs by
growing corn plants in a greenhouse. These plants showed no evidence
of "Cs uptake; however, the quantity of forage which could be grown
was limited, resulting in small samples.
Calculations from our data on pasture soil and forage indicated
that soil uptake was small compared to direct foliar absorption. The
mean value of pasture-forage activity during 1964 was about 400 pe/m’.
The cumulative soil activity was about 80,000 pc/m’, Therefore up-
take of 0.5% would account for all of the pasture activity, or 0.1%
uptake would account for all the activity in third-cutting 1964 hay
(Table 1). Relations between rainfall and forage activity suggested
that soil uptake is probably of the order of 0.01% and therefore negli-
ble, for example, in the case of first-cutting hay (Table 1).
Deposition coefficients between rainfall and plants were calculated
from the ratio of '"Cs precipitation deposition per square meter to
the activity found in forage per square meter. Considerable variation
was expected in the coefficients because of the uncertainties involved
in comparing rainfall and plant activities. When relatively long intervals
occurred between rains, plant growth tended to dilute the activity
already present in plants; this was particularly true when the pastures
were irrigated. Significant deposition of ‘’Cs from air or dust is a
possibility, but we have been unableto clarify this point with our data.
Table
1 presents the deposition coefficients found by comparing
cumulative fallout during the growing period with activity per square