Influence of Soil Moisture Content and Manuring Condition on Exudation of Soybean.

Abstract

Using soybean variety Norin No. 2 grown under light and heavy manuring condition by pot culture, exudation was investigated under three levels of soil moisture content (Fig. 1). Soybeans were planted on May 25, and these plants were treated with dry, medium and wet soil conditions from June 22 to July 6. Except the treatment periods, they were maintained under medium soil moisture condition. The exudates were taken from detopped plants at several growing stages, and determined their volume and several inorganic components. The results obtained were summarized as follows; 1) Concerning the exudation power of soybean varies at each growing stage. In early vegetative stage, it gradually increases, and in the flower initiation stage, it shows maximum value, but thereafter it gradually decreases (Fig. 3). 2) In plants treated with dry soil condition the exudating power shows remarkable small value, but it recovers in comparatively short period when the plants were return to the medium soil moisture condition. While in plants treated with wet soil condition it does not show and distinct change (Fig. 3). 3) The exudating power of soybean plants is approximately parallel with the function of the root respiration, if these plants were at the same growing stage, or were grown under the same soil moisture condition (Table 3 & Fig. 6). 4) The concentration of each inorganic component in exudate is higher in plants treated with dry soil condition, but it is somewhat lower in plants treated with wet soil condition than with medium soil moisture condition (Table 1 & 2). By reason of difference in amount of exudate between soil moisture treatments, it is considered that the whole quantities of each nutrient translocated to top are decreased by dry treatment, while no decrease is occurred in wet treatment. 5) In the plants grown in heavy manuring condition, the root contains more amount of protein-N (Fig. 5), the respiration of root is more active (Fig. 4), the amount of exudate is more abundant (Fig. 3), the concentration of NH4-N, P, K and Mg in exudate is higher (Table 1 & 2) and the growth of top and root is more vigorous than in the plants grown in light manuring condition. Such heavy manuring condition in soybean plant will be efficient to lighten the drought damage, to hasten the recovery from such damage, and moreover to change the weak growth brought by wet soil condition to vigorous growth.