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sEcrion 12
were very high, especially in the lower leaves, in which Ca ranged from 690 to
980 meq per 100 gm of dry tissue.
Analyscs of Leaf Tissue Collected on Rongelap Atoll
Foliage samples have been collected in the field, primarily from woodyplants,
which dominate the atoll environment.In most cases separate samples were taken
of the upper and the lower foliage of the plants. Representative values for K
and Cs-137 in three of the commonspecies are given in the lower part of Table1.
Potassium contents of the upper foliage have consistently proved to be much
higher than thosein the lowerfoliage. On the other hand. Ca and Mglevels have
been consistently higher in the lower than in the upper leaves. In the case of
Cs-187, the pattern is consistent in the samples of a particular species, but there
are differences between the species. In Messerschmidia and Pandanus, Cs-187
levels are higher in the upper than in the lower foliage, which is the same pattem
that was observed in the squash grownin the greenhouse. In contrast, Scaevola
shows higherlevels of Cs-137 in the basal than in the upperleaves.
In one instance the effect of mineral fertilization in the field was tested. Two
1/80 acre plots in a coconut grove on Rongelap Island were treated with a broad-
cast application of KCl in August 1958,at a rate of 140 pounds k2Operacre. The
dominant ground vegetation, a grass (Lepturus sp.), was sampled in March 1959
from thefertilized and control areas. Average values for the content of K(meq per
100 dry gm) and Cs-187 (d/m/gm) were as follows: Control—10.1 K, 65 Cs-137;
Fertilized—16.5 K, 20 Cs-137. Samples from the same locations collected in
September 1959 showed no significant difference in either K or Cs contents,
however, and so the depressive effect of the K fertilization on Cs-137 was
apparentlytransitory, although the possibility of seasonal differences exists.
DISCUSSION
N, P, and fertilization in various combinations depressed the uptake of Cs-187
in all cases in the greenhouse experiments. It was clear that dilution byincrease
of dry yield withfertilization could not explain the reduction of the Cs-137 levels,
but no gencral explanation for the effects of the three elements can be given at
this time. One fact of possible interest in this connection was the considerably
higher uptake of K which was observed with the P-K treatments (i.e. without
N) with both squash and tomato.
The results of the pot cultures do not distinguish clearly between the effects
- of the differentfertilizer elements on Cs-137 content of the plants, since no treatments involved single elements. There was an indication in the tomato that high
Kk content was associated with lower Cs-137 content. but this was not confirmed
by the tests using squash. A possible explanation for this difference lies in the
fact that tomato responded in yield to K additions but squash did not. In the
fertilization with K in the field, at least a temporary depression of Cs-137 uptake
was effected. This is consistent with the results of Nishita et al. (1960), who
observed a decreased absorption of Cs-187 with K fertilization of soil which was
low in K. The Rongelapsoils are lowin K as evidenced bysvil analyses and by
the very lowlevels of K in the older leaves of the plants growing on them.
The differences between upper and lowerfoliage in their content of the various
ions are of special interest. The most usual pattern shows both K and Cs-187
higher in the upper Iecaves than in the lower leaves. Field-collected Scaevola