' Table 2. Distribution coefficients (K,) of untreated Aiken clay and CH flooH-NA OH systems. loam under HNO,-NaOH 3 3 4 CH.,COOH-NH OH System HNO,-NaOH System pH 0.67 pH K, x10" Ky x 104" 2462.4 + 841.3 2.55 45.9 + 2.5 2.32 44.8 + O.1 3.81 46.3 + 2.0 3.20 7.74 G4 4.76 65.3 + 0.7 3.75 2.7 + 0.5 5.77 31.8 + 0,02 4.61 1.2 + 0.06 6.54 13.1 + 0.5 6.27 0.6 + O.1 7.69 2.7 + 0.4 6.96 0.5+ Q.1 B.76 0.5 + 0.2 7.58 6.0 + 3,1 10.02 0.4 + 0.1 8.16 16.1 + 0.0 11.57 44.0 + 0.4 9.84 39.4 + 3.9 11.00 39.4 + 3.9 12.19 171.1 +t 2.6 13.55 113.5 + 6,3 range (pH 4-7), the movement is likely to with decreasing pH. In the minus organic complexing agent is likely to enhance the extent in the acidic pH range than in the of organic matter. be slow, but it is likely to increase matter soil, the addition of a movement of Am to a much greater soil containing appreciable amounts Since the movement of Am is related to its availability to plants, the statements made above apply also to Am uptake by plants, insofar as they pertain to the pH range for normal plant growth. As pointed out previously (Nishita, 1976), the pH range for productive plant growth is between pH 3 and pH 10 (Arnon, Fratzke, and Johnson, 1942; Arnon and Johnson, 1942; Small, 1954). At both ends of this pH range, the plants generally encounter adverse soil conditions for normal growth, so the optimal range is usually narrower. In summary, several soil components, particularly the organic matter, were found to influence the extractability of **!Am as a function of pH. The implications provided by this study appear to be interesting to test under environmental conditions. FUTURE PLANS The study described here will continue with 233pu and 237Np. ACKNOWLEDGMENTS The authors wish to thank R, M, Haug and T. Rutherford for the chemical analysis of soil] materiais and A. J. Steen for counting the samples on the alpha spectrometer. These studies were supported by Contract E(04-1) GEN-12 between the U.S. Energy Research and Development Administration and the University of California. *kAverage of 2 samples with standard deviation 90 91