1364 sicrion 12 reduced the content of Cs-187 in the tissue. Also reported are the results of a field experiment on Rongelap Island in whichfertilization with KCI at least tem- porarily reduced the content of Cs-187 in a native grass. Potassium and Cs-13% contents of foliar samples of several woody species collected on Rongelap Island are also included. In the most common pattern, K and Cs-137 contents of the upper foliage were higher than those of the lower Icaves, but one species con- sistently showed higher K but lower Cs-157 in the upper foliage. LowK status of the soil and differences in mobility within the plant may explain these patterns. INTRODUCTION AND METHODS The data reported here concern the uptake of Cs-187 by plants from soils of Rongelap Atoll, Marshall Islands, with special reference to fertilization of the soil with N, P, and K. The report includes the results of greenhouse pot culture tests using Rongelaptop soil, as well as foliar analyses of native vegetation growing on the atoll. Rongelap Atoll was contaminated by radioactive fallout on March 1, 1954. The principal radionuclide found in plant tissues in 1958 and 1959 was Cs-137. Radionuclides in the soil remain in the top few inches with 90% or moreof the radioactivity in the top two inchesorless. In the current greenhouse studies, tomato and squash plants were grown in carbonate fragments derived from corals and foraminifera, into which is incor- . Seattle on top soi! (0 to 10 inches) collected in a coconut grove on Rongelap Island. The soil (perhaps better called soil material) consists entirely of calcium porated about 9% organic matter. In the rather coarse unsieved field soil the pHis 5.0; the cation exchange capacity is attributable entirely to the organic fraction and is about 8 meq per 100 gm; among the exchangeable cations there are about §0% Ca, 15¢ Mg. 4 Na, and 0.7% K; the soil is coarse, very friable. and highly porous. The pot culture technique was essentially that of Jennye¢ al. (1950). Fertilizer solutions were mixed with 667 gm portions of soil which were placed into 6-inch plastic pots, uniform seedlings were transferred to the pots, and the plants were watered with distilled water as needed. Plants were harvested after about 30 days, and the tissue oven-dried and ground. The Cs-137 content of the dry material was determined by gamma ray spectroscopyusing a threc-inch thallium- activated sodium iodide crystal in conjunction with a multichannel analvzer. Tissue was drv ashed and the acid solution analvzed for potassium bytitration of the cobaltimtrite precipitate with permanganate. Samples collected in the held usually included leaves from the upper (younger) and lower (older) foliage, und were composite samples from several plants in the vicinity of a collecting point. The tissue was oven-dried in the field headquarters. and was subsequently re-dried, ground, and analyzed in the same manner as the greenhouse samples. Greenhouse Experiments RESULTS In a prehminary experiment with tomato, vanety Marglobe, the fertilizer treat- ments and the Cs-137 in disintegrations per minute per gm drytissue were: nfertilized control, 490; N-P-k, 100; N-P, 190; N-K, 240; P-K, undetectable. These results are particularly interesting because all fertilizer additions depressed the uptake of cesium. There was marked response in vield to the nitrogen and ~~