Studies on the Dry Matter Production of Sweet Potato : IV. The relation between the concentration of mineral nutrients in plant and distribution ratio of dry matter produced.

Abstract

The relationship between the concentration of nutrients in plant and distribution of dry matter produced has long been recognized. It was decided, therefore, to investigate further this problem as in the previous work the role of these nutrients was not clearly understood. The distribution ratio of dry matter produced was defined as the ratio of the increase in weight of each part to that of the total dry matter during a unit period. 1). There is a close relationship between the distribution ratio of dry matter to the top and nitrogen concentration in leaves under different potassium levels as shown in figure 2. The distribution ratio of dry matter to the top shows an increase with the increase of nitrogen concentration in leaves. But in the case of high potassium level, the distribution ratio to the top is considerably less than that of low potassium level even if the nitrogen concentration is exactly the same. Consequently, it was considered that potassium was effective for translocation of assimilates from the top to the tuberous roots. 2). At the early growing stage, as the relative rate of the increase of nutrients was more than that of the dry matter produced, the concentration of nutrients in plant increased, and it is shown for nitrogen in figure 4. As nitrogen concentration in plant increased, the leaf area ratio which constituted the relative growth rate with the net assimilation rate, increased and it caused great increase of the relative growth rate of dry matter under the condition of less leaf area index at early growing stage. 3). At the late growing stage, the decrease of the concentration of nutrients in leaves is mainly due to the translocation of nutrients contained in the leaves and the other parts of plant to the tuberous roots. It is desirable to keep high potassium concentration for maintaining vigorous photosynthetic activity, and therefore, it is necessary to prevent the decreasing of potassium concentration in leaves by applying potassium at the late growing stage.