Suppressive effect of rice bran incorporation in paddy soil on germination ofMonochoria vaginalisand its relationship with electric conductivity

Abstract

Laboratory experiments were conducted to investigate (1) the effects of the addition of rice (Oryza sativa. L.) bran to paddy soil on the germination of Monochoria vaginalis (Burm. f.) Kunth, and (2) the relationship between the electric conductivity (EC) of the soil solution and germination. Soil samples were collected at 4 sites in Japan. After flooded soils with rice bran had been incubated for 7 d at 30 C, the soil solution was collected using a porous cup and the EC of the soil solution was measured. The amounts of rice bran added to the soil were 0%, 0.3%, 0.6% and 0.9% (weight(w)/w). In the soil solution obtained, seeds of M. vaginalis were incubated for 3 d at 30 C, and the germination percentage was then analyzed. The addition of rice bran suppressed germination, and the degree of suppression increased with increasing content of rice bran. Although the same amount of rice bran was applied to each soil, the degree of growth suppression by rice bran as well as the EC of the soil solution differed among the soils. In each soil, there was a positive correlation between the amount of rice bran and EC, and the degree of growth suppression significantly increased with an increase in EC. When EC was higher than 150 mS m À1, seeds of M. vaginalis hardly germinated. There was no significant correlation between the oxidation-reduction potential (Eh) of soil and seed germination, suggesting that EC is a more reliable and convenient indicator than Eh for evaluating the relationship between the addition of organic material and seed germination. In conclusion, the addition of rice bran to soil increases the EC of the soil solution, and EC is one of the factors that suppress the germination of M. vaginalis. The suppressive effect of rice bran on germination is different among soils. This fact is attributed to the difference in EC due to the addition of rice bran. Thus, it is expected that EC can be used as an indicator for determining how much rice bran to add.

Effects of poultry manure on soil solution electrical conductivity and early growth of Monochoria vaginalis

“…The soil solution EC (SSEC) is highly correlated with other soil properties, including the level of organic matter and salinity, which also affect crop productivity (Grisso, 2009). The application of rice bran also increases SSEC, suppressing the germination of M. vaginalis (Nozoe et al, 2012). Since PM is also organic matter similar to rice bran, its application may increase SSEC and reduce the occurrence of M. vaginalis.…”

“…In organic rice farming where no herbicides are applied, rice bran is often used for weed control. The addition of rice bran to the soil increases its electrical conductivity (EC) (Nozoe et al, 2012). The soil solution EC (SSEC) is highly correlated with other soil properties, including the level of organic matter and salinity, which also affect crop productivity (Grisso, 2009).…”

Relationship between physical property of soil and growth ofMonochoria vaginalisunder paddy condition of organic farming—analysis using settled soil volume in water of superficial layer.

“…We have reported that EC increased with the decrease in soil Eh (oxidation-reduction potential) (Nozoe et al, 2012), and Nakai and Toritsuka (2009) have reported that the decrease in soil Eh with rice bran was completed over a 4-day period of cultivation. Presumably, the suppression of M. vaginalis with the increase in EC began immediately after transplanting.…”

“…Although many factors, some unknown, could be associated with the decrease in the number of the M. vaginalis with the application of rice bran, these factors have not been identified. In the previous report, we suggested that the addition of rice bran to flooded soil suppressed the germination of M. vaginalis (Nozoe et al, 2012) and also that the EC of the soil solution is useful as a chemical indicator of the suppression of M. vaginalis growth. Generally, the amounts of substances such as Fe 2+ (Nozoe et al, 2008) and aromatic carboxylic acids (Tanaka et al, 1990) increase in flooded soil, and these substances sometimes suppress the growth of paddy rice.…”

“…However, identification of an appropriate soil property indicator correlated with the growth of M. vaginalis has received little attention. In our previous study, we reported that the addition of rice bran increased the electrical conductivity (EC) of the soil solution and that there was a negative correlation between the EC and germination of M. vaginalis (Nozoe et al, 2012). The increase in EC was suggested to be associated with amounts of toxic substances such as ferrous iron (Fe 2+ ) and organic acids that impaired the germination of M. vaginalis.…”