241Am availability to plants as influenced by chelating agents

The ability of some chelating agents, especially that of DTPA (diethylene triamine pentaacetic acid), to increase plant uptake of 241Am has been previously reported and further studied. In one experiment, bush bean, barley, and two corn hybrids were grown with and without DTPA in a calcareous soil of pH 7.5 (Hacienda loam) and a noncalcareous soil of pH 6 (Yolo loam). There were plant species differences in both uptake and distribution of 241Am. With bush beans and corn, the 241Am was concentrated in the upper parts of the plants. About 2.5 times as much 241Am was in leaves of bush beans grown in Hacienda loam as in Yolo loam; with corn the ratio for 241Am in shoots for the same two soils of different pH was from 9 to 20. Barley was different in that more 241Am was in plants at the low soil pH than in the high, and there was a more uniform distribution throughout the plants. In bush beans there was much less 241Am in seed pods than in leaves. The discrimination ratio for 241Am when plants were grown in soil was as much as 7 when DTPA was present. DTPA (10-3M) extracted 25 percent of the 241Am from the Hacienda loam and 60 percent of it from the Yolo loam. Nitric acid was more efficient than DTPA as an extracting agent. An experiment was conducted in which four new Fe chelates were compared with FeDTPA in their ability to increase 241Am uptake from the two different soils. Three of these Fe chelates had very little effect, but an Fe chelate of the phosphine type was about 2.5 percent as effective as was FeDTPA