Promotive effect of soil solution on germination of Monochoria vaginalis under paddy conditions

ABSTRACT

Growth of the weed Monochoria vaginalis (Burm. f.) Kunth under the conditions of organic rice production is a serious problem. The reason for the growth of M. vaginalis being dominant, especially in organic rice production, is not fully understood. In this study, laboratory experiments were conducted to analyze soil and seed factors in relation to the promotion of germination. (1) After incubation of flooded soil with or without the addition of rice bran (0.3%, 0.6%, and 0.9% in an air-dried soil basis), soil solutions were recovered and seeds of M. vaginalis were incubated in the soil solutions. Germination in the soils solutions without and with 0.3% rice bran was greater than that in distilled water. However, germination was suppressed in the presence of 0.6% and 0.9% of rice bran. These findings indicate that the solution from the soils with rice bran has different effects that may either increase or decrease germination. (2) A mixture of air-dried soil and distilled water was filtered to obtain a soil solution. Seeds were incubated in the soil solution (same as above). Environmental and physiological factors affected germination: exposure of seeds to light was an environmental factor and high germination activity and shallow dormancy of seed were physiological. The recovered soil solution promoted germination when these factors were not optimized. (3) There was a negative and significant correlation between dissolved oxygen (DO) in the soil solution and germination, indicating that a low content of DO was a promotive factor for germination. (4) Based on an experiment using pH buffers, germination increased with decrease in pH of soil solution, as long as the pH ranged from 4.0 to 7.0. This finding indicates that pH is also a factor that promotes germination.