1366
secrion 12
were very high, especially in the lower leaves, in which Ca ranged from 690 to
980 meq per 100 gm ofdry tissue.
Analyses of Leaf Tissue Collected on Rongelap Atoll
Foliage samples have been collected in the field, primarily from woody plants,
which dominate the atoll environment. In most cases separate samples were taken
of the upper and the lowerfoliage of the plants. Representative values for K
and Cs-137 in three of the commonspecies are given in the lower part of Table 1.
Potassium contents of the upper foliage have consistently proved to be much
higher than those in the lowerfoliage. On the other hand, Ca and Mg levels have
been consistently higher in the lower than in the upper leaves. In the case of
Cs-137, 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 lowerfoliage, which is the same pattern
that was observed in the squash grown in the greenhouse. In contrast, Scaevola
showshigherlevels of Cs-137 in the basal than in the upper leaves.
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 broadcast application of KC] in August 1958, at a rate of 140 pounds K;O peracre. 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-137 (d/m/gm) were as follows: Control—10.1 K, 65 Cs-187;
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
apparently transitory, although the possibility of seasonal differences exists.
DISCUSSION
N,P, and fertilization in various combinations depressed the uptake of Cs-137
in all cases in the greenhouse experiments. It was clear that dilution by increase
of dry yield with fertilization could not explain the reduction of the Cs-137 levels,
but no general 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 different fertilizer elements on Cs-137 content of the plants, since notreat-
ments involved single elements. There was an indication in the tomato that high
K content was associated with lower Cs-187 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-137 with K fertilization of soil which was
low in K. The Rongelap soils are low in K as evidenced by soil analyses and by
the very lowlevels of K in the older leaves of the plants growing on them.
The differences between upper and lower foliage in their content of the various
ions are of special interest. The most usual pattern shows both K and Cs-137
higher in the upper leaves than in the lower leaves. Field-collected Scaevola