Influence of Soil Moisture Content on the Growth and Yield of Soybean. : (V) Changes of carbohydrate and nitrogen in soybean plant as affected by deficient or excessive soil moisture contents at various growing periods.

Abstract

The object of this study was to trace the changes of carbohydrates and nitregen in soybean plants grown under deficient or excessive soil moisture conditions during the early vegetative, flowering and ripening periods, respectively. During the other periods, the soil moisture for the experimental plants were maintained at the same level with those for the control plants. The results obtained are summarized as follows ; 1) The total sugar content in the leaves and the stems increased in the plants under deficient soil moisture conditions, while the starch content increased abnormally in the plants under excessive soil moisture conditions. The nitrogen content in each organ decreased in all the treated plants. 2) Absorption of nitrogen was inhibited both by deficient and by excessive soil moisture conditions, and the degree of inhibition was greater in the series treated during the flowering period than in that treated during earlier periods. Accumulation of carbohydrates in plants was reduced by deficient soil moisture conditions but remarkably higher amount of carbohydrates accumulated in the plants under excessive soil moisture conditions. The degrees of inhibitionor of accumulation were also higher in the series treated during the flowering period than in those treated at the other periods. 3) In the plants under deficient soil moisture conditions during each period and under excessive ones during the earlier period (plant about 20 days after the flowering time), the amounts of total sugar and starch in leaves and stems were smaller than those in the control plants. And, the amounts of those matters translocated from the leaves and the stems to the pods were also reduced in the treated series. On the contrary, in the plants grown under excessive soil moisture conditions during the flowering or ripening periods, the most part of carbohydrates in the pods appeared to have been translocated from the leaves and the stems. However, the accumulation of nitrogen in vegetative organs and the amount of nitrogen translocated to sexual organs reduced in every treated series. In the treated plants, in general, large parts of carbohydrates and nitrogen in the pods depended on assimilation and and absorption after the flowering period. 4) In the plants under deficient or excessive soil moisture conditions during the earlier periods, vegetative growth was retarded and consequently the number of flowers was very few ; but the percentages of flower- and pod-shedding were only little different compared with those in the control plants. In the plants treated with deficient or excessive soil moisture conditions during the flowering period, the number of flowers produced was almost the same as that in the control plants, but the shedding percentage of the former was much higher.