The absorption, distribution, and redistribution of15N-labelled ammonium and nitrate nitrogen administered at different growth stages of rice

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Abstract
A tracer technique was used to study the absorption, distribution, and redistribution of nitrogen from 15N-labelled ammonium and nitrate administered at different growth stages of rice. The plants absorbed nitrogen from both the sources quite rapidly during the early stages of growth. At the young panicle formation and booting stages the nitrogen from ammonium was translocated more to the youngest growing leaf while that from nitrate to the newly developed one which had the highest nitrogen content. After the emergence of panicle at the booting stage there was a considerably higher distribution of nitrogen, in both the flag leaf and panicle, from ammonium compared to that from nitrate. In the middle leaves there was an equal distribution of nitrogen from both ammonium and nitrate while in older leaves, nitrogen from nitrate was more prevalent. At harvesting, panicles of the plants which were supplied nitrogen at the young panicle formation stage had an equal redistribution from ammonium and nitrate. But, in case of nitrogen application at the booting and milk stages, the redistribution into the panicle was greater from nitrate than from ammonium. An aspect of different paths for ammonium and nitrate nitrogen transport from root to shoot is discussed.