Studies on a New Herbicide, Oxadiazon (G-315, 17623-RP)

IV. Influence of Soil Properties on the Herbicidal Activity of Oxadiazon under Flooded Conditions of Paddy Field

Abstract

Using 29 types of paddy field soils collected from public agricultural experiment stations in Japan, both herbicidal activity on barnyardgrass (Echinocloa Crus-galli) and phytotoxicity (the length of browning of leaf sheath) against transplanted rice of oxadiazon were examined.
1) The herbicidal activity of oxadiazon was significantly correlated with oxadiazon concentration equilibrated in water (adsorption), pH and C. E. C. of soil. The phytotoxicity of oxadiazon was significantly correlated with oxadiazon concentration equilibrated in water, clay content and bulk density (volume weight) of soil.
2) The herbicidal activity was significantly correlated with the phytotoxicity against transplanted rice; this means that, in the soils in which oxadiazon showed the high herbicidal activity, the influence on transplanted rice also seemed to be large.
3) Oxadiazon concentration equilibrated in water was significantly correlated with clay content, C. E. C., bulk density of soil, but was not significantly correlated with organic matter.
4) Although, in the case of the correlation except black volcanic ash soils, organic matter was highly correlated with herbicidal activity, phytotoxicity and oxadiazon concentration. It was showed that organic matter acted an important role for adsorption of oxadiazon.
5) The adsorptive ability of compost of rice plant, peatmoss, cellulose and bark compost was much higher than that of bentonite, zeeklite and allophane. The adsorptive ability of oxadiazon by organic matters was as follows; peatmoss>bark compost>compost of rice plant>>cellulose. The adsorptive ability by cellulose was remarkably low. The adsorptive ability of oxadiazon by clays was as follows; allophane>bentonite>zeeklite. The difference of them was not remarkable.
6) The results of 4) explain the reason why there was no observable correlation between oxadiazon concentration equilibrated in water and organic matter content for the different soils used in this study may be interpreted by the difference in adsorption of oxadiazon among the different organic matters contained in the individual soils.
7) Bulk density of soil, which is significantly correlated with clay and organic matter and can be easily measured, may be an available guideline which shows the practical variation of the herbicidal activity and phytotoxicity of oxadiazon in soil.