Table 1. AVERAGE C.ESIUM-137 Pc,/@ POTASSIUM IN DRIED MILK PRODUCTS
AND PRECIPITATION FOR MILK SAMPLING STATIONS IN THE NORTHWESTERN UNITED STATES, JANUARY 1959-JUNE 1960, GROUPED ACCORDING
TO NATURAL VEGETATION ZONES
Vegetation
zone
Sample station
No.of
samples
Coniferous Portland, Oreg.
forest
Burlington, Wash.
65
75
tirasslaud Bismarck, N.D.
Bottineau, N.D.
Mitchell, 5.D.
Cando, N.D.
67
a
58
31
Sagebrush
78
70
73
73
Sunnyside, Wash.
Payette, Ida.
Idaho Falls, Fda,
Monroe, Utah
Precipitaavg. ¥7Cs tion total
°% of ppt
in winter
pe./g K
inches
39
92
67
55
32
47
2
29
37
—_
avg. 29
9
18
9
lo
4
12
_
avg. 90
65
51
42
48
avg. 54
22
43
49
34
avg. 37
avg. 6]
avg. 12
months
55
49
28
_
near the milk sampling stations showed the coniferous
forest zone stations as receiving an average of 61 in. from
January 1, 1959, until June 1960. This was compared with
an average of only 29 and 12 in. from grassland and sagebrush zones respectively. It is realized that precipitation
readings from a few stations probably do not represent
an accurate measurement of the precipitation over the
entire milk harvest areas; nevertheless, natural vegetation
reflects the biological effectiveness of precipitation and the
boundaries of these may be used to delimit long-term
biological climates. It has long been recognized by plant
ecologists that total annual precipitation in the northwestern United States is not sufficient to differentiate
sage-brush and grassland zone climates*. The seasonal
distribution of precipitation in the sage-brush zoneis
concentrated in winter months, while that of the grassland
zone is concentrated in spring and summer (Table 1).
Seasonal precipitation could greatly influence the amounts
of cxsium-137 deposited on foliar surfaces. In temperate
climates having a definite seasonal agricultural yield foliar
deposited cxsium-137 reflects the amounts largely accumulated during the summer photosynthetic period. Forages
grown in the semi-arid sage-brush zone seldom experience
summer precipitation and growth water is supplied by
irrigation. In the grassland zone growthof forage crops
and summerprecipitation coincide to yield higher czesium137 values in contrast to the non-synchronyof biological
and meteorological events and lower cxesium-137 values in
the sage-brush zone.
The higher average cesium-137 content of dried milk
products produced in the moist forest zone appears
related to the greater precipitation in this zone in contrast
to the grassland and sage-brush zones. The lower average
czsium values in milk products produced in the sagebrush zone in contrast to grassland zone appear as a result
of a non-synchrony of phenological and meteorological
events induced by land management practices.
To test statistically the effect of vegetation zones in