抄録
The herbicidal mechanism and its effect was elucidated in a paddy rice field by applying distilled spirit waste (DSW) and rice bran (RB) to flooded waters, immediately after transplantation. Release of nutrients from organic materials and their soil concentration were also investigated.
1) Application of RB (2000kg ha-1) and DSW (3000kg ha-1) significantly decreased (p=0.05) the dry weight of weeds when compared with the untreated control. Between the two most common weeds, Echinochloa crus-galli Beauv. var. oryzicola Ohwi and Scirpus juncoides Subsp., DSW application decreased the dry weight weeds, whereas RB application affected only the former.
2) Organic materials decreased the redox potential of the soil 3-19 days after application, suggesting a deficiency of dissolved oxygen (essential for weed growth) in soil.
3) Anaerobic fermentation of organic material by soil microorganisms resulted in production of isobutyric acid in flooded water. A sharp concentration peak of isobutyrate was observed 7 days postapplication. A high negative correlation (r2=0.808, p=0.0024) was observed between the integrated concentration of isobutyrate and the dry weight of weeds. Production of the organic acid was considered as an important factor in the herbicidal mechanism.
4) After amendment with organic materials, the electrical conductivity of soil sharply increased, indicating the release of a large amount of water-soluble substances. Furthermore, application of organic materials markedly increased the soil concentration of ammonia, potassium, calcium, and magnesium. The usefulness of DSW and RB as nutrient amendment can be confirmed 20 days after application.
