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Suggested Citation:"MANAGEMENT." National Research Council. 1963. Behavior of Radioactive Fallout in Soils and Plants. Washington, DC: The National Academies Press. doi: 10.17226/18567.
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Page 18
Suggested Citation:"MANAGEMENT." National Research Council. 1963. Behavior of Radioactive Fallout in Soils and Plants. Washington, DC: The National Academies Press. doi: 10.17226/18567.
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Page 19

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18 VIII. MANAGEMENT A. The Effect of Liming The effect of calcium on strontium uptake has been discussed to some extent in two previous sections. A practical application of this is in the liming of acid soils. The uptake of strontium from different soils increased in proportion to the reciprocal of the exchangeable calcium (24, 66). No relation has been found between the total calcium or calcium carbonate content and strontium uptake (22, 30). Since soils have finite exchange capacities, overliming has little additional effect on strontium uptake. This is demonstrated by the application of lime to neutral or alkaline calcareous soils, which reduces the strontium uptake only slightly (30, 98, 105, 139). A fourfold re- duction of strontium uptake by liming acid soils is generally the most to be expected (109, pp. 18-49). The ratio of radioactive strontium to calcium in the plant is as important as the radioactive strontium concentration because deposition of radioactive strontium in animal skeletons depends on the calcium content of the diet (18). Liming tends to decrease this ratio until the exchange capacity of the soil becomes saturated with bases. Then, when the soil is no longer acid, additional lime remains undissolved and thus unavailable to the plant. Therefore, although liming serves a twofold purpose of reducing both the strontium concentration and the strontium-to-calcium ratio, the lowest values for both are usually achieved at a point that coincides with the amount of lime needed for maximum crop yields. B. Fertilizers In some experiments, fertilizer has increased the uptake of fission products, but in others no increase occurred (14, 47, 117, 120). Fertilizers and manures may affect the availability of the fission products, as discussed in previous sections, but it is possible that better plant growth will obscure any other effect. C. Cultivation Cultivation tends to increase strontium uptake by some crops (14), possibly by providing more root contact. Greater uptake of calcium results from a completely mixed calcium application than from a banded application (12). Increased uptake of strontium in the second year of a field experiment has been attributed to a more uniform distribution of strontium (14). In the case of shallow-rooted grasses, as dis- cussed under species differences, it appears that plowing reduces the strontium-90 to calcium ratio of the new planting (72).

19 Plowing surf ace-contaminated fields to a depth of seven inches resulted in 50 per cent of the activity in the zero- to four-inch level. Both rotary tillage to four inches and two plowings resulted in>70 per cent of the activity in the top four inches (110). The uptake of fission products placed at a 60-cm depth, compared to a 30-cm depth, was as low as one thirtieth in the tops and one tenth in the seeds of oats and peas (36). D. Moisture Variations in the soil moisture tension were found to affect cesium uptake and the cesium-to-potassium ratio, but no effect was noted on calcium and strontium (125). Several observations (128, 129) of a tenfold greater uptake of cesium by low- land rice than by upland rice have been made. Evidence indicates that increased amounts of ammonium ion under the reduced conditions caused the greater uptake. E. Prolonged Cropping Little variation in strontium availability is observed over a period of years (14, 43), and the uptake of strontium per unit weight is fairly constant (86). The effect of fixation has not been studied sufficiently in the field to determine whether it is important under prolonged cropping. The uptake of cesium increased under prolonged cropping (86), probably because the potassium became depleted by crop removal.

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