ABSORPTION OF IRON FROM FINELY GROUND MAGNETITE BY CITRUS SEEDLINGS

Abstract

Expts. in which finely ground magnetite was used as a source of Fe in sand cultures for citrus seedlings indicated that the absorption of Fe from this compound is made possible by the formation of intimate contacts between root and iron oxide particles, in which conditions for the extraction or solution of Fe must differ from those prevailing in the external nutrient soln. With an amt. of magnetite sufficient under ordinary conditions (0.1%), addition of CaCO3 brought about Fe deficiency; however, with more magnetite, the plants were again able to secure adequate Fe, despite the presence of CaCO3. In cultures containing CaCO3 and 0.1% magnetite, less frequent flushing enabled the plants to secure adequate Fe, whereas frequent flushing brought on Fe chlorosis. This was shown to result from pH differences which develop when the frequency of flushing is varied. These results emphasize the view that the "soil solution" consists of 2 separate, though not altogether independent, parts: the heterogeneous, intimate contact zones between roots and soil particles; and the external soln. Under conditions of ample moisture supply, these 2 parts are, to some extent at least, intercommunicating and capable of influencing each other.