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RAINFALL (INCHES/YEAR) 1955-1957
70
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Fig. 4—Correlation of soil Sr* and rainfall.
the divergence between the micromicrocurie per square meter on adjacent new and old growth.
This suggests that micromicrocurie per kilogram or micromicrocurie per gram of Ca is the
best unit for expressing the activity of vegetation when the conditions of growth are uncontrolled.
In Fig. 5 the micromicrocurie per gram of Ca (S.U.) in vegetation at all stations in mid1956 is correlated with the calcium content of the top 4 in. of soil. In making the comparison
the variation in total fallout of Sr*® (uc /m’ in soil) has been allowed for by normalizing the results of the various stations to a nominal fallout of 5000 puc /m’. Thusfor station B, at which
the Sr®° in soil was 6600 uuc/m’, the vegetation result given in Table 2 has been multiplied by
the factor 5000/6600 before insertion in Fig. 5. The object of normalizing the results in this
way is to avoid spurious correlation due to the association of high rainfall both with high total
fallout and with low soil calcium and pH.
The normalized 8.U. ratio in grass does not show any correlation with soil calcium when
the latter is 1 g/kg dry weight or over, as determined by HCl extraction. Thus the normalized
S.U. in grass from Pwllpeiran (A3) and from Chilton (K) are about the same, though the soil at
the former station has 1 g of Ca per kilogram and pH 4.9 whereas the latter has 156 g of Ca per
kilogram and pH 8.0.
The normalized S.U. values in vegetation on the uncultivated, acid, and very low calcium
soils Al, A2 and E are higher by a factor of 10 to 60 than the values for normalsoils.
Romneyet al. (1957) grew crc = in pots containing 7 different soils to which Sr*° had been
added. The highest Sr*° levels we: ound in plants grown in acidic soils low in calcium and the
lowest levels in the alkaline calcareous soils. Piants grown in the Sassafras soil, which hada
pH of 4.6 and less than 0.1 g of exchangeable Ca per kilogram, took up about 10 times as much
Sr*” per unit dry weight as plants grown on alkaline calcareous soils. These experiments were
under controlled laboratory conditions, using Sr°’ added uniformly to homogenized soil, and
without the complications introduced by foliar uptake, the profile of Sr®° in uncultivated soils,
and the presence of peaty matt between vegetation and soil.
215
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