ACCUMULATION OF CARBON AND NITROGEN-COMPOUNDS IN SWEET-POTATO PLANTS GROWN UNDER DEFICIENCY OF N, P, OR K NUTRIENTS

Sweet potato (Ipomoea batatas L. var. Beniazuma) plants were grown in the field of Hokkaido University where the following treatments: (1) a pplication of nitrogen, phosphorus, and potassium (C plot), (2) absenc e of nitrogen application (-N plot), (3) absence of phosphorus applica tion (-P plot), and (4) absence of potassium application (-K plot) hav e been maintained for 76 y. Results obtained were as follows. 1) Under nitrogen deficiency, total dry weight and tuberous root dry weight de creased. Harvest index for dry weight in the -N plot was highest, whil e the harvest index for nitrogen was the lowest among the treatments, suggesting that high nitrogen use efficiency was achieved in the -N pl ot. 2) Under phosphorus deficiency, total dry weight was the same as t hat in the C plot, while tuberous root dry weight was strictly restric ted, suggesting that the construction of proteins or cellulose in leav es was stimulated, and the construction of starch in tuberous roots wa s restricted in the -P plot. 3) Under potassium deficiency, since nitr ogen absorption was not restricted compared with the control, and phos phorus absorption was restricted, the nutritional status of the plants showed a nitrogen excess, suggesting that nitrogen excess and disorde r of phloem transport adversely affected the sweet potato growth.