Effect of Soil Application of Several Herbicides on the Initial Growth of Direct Seeded Rice Sown at Different Depths under Flooded Paddy Conditions

Abstract

Effect of soil application of several herbicides on the initial growth of shoots and roots in direct seeded rice seedlings sown at 0cm and 1cm depths under flooded paddy conditions was investigated.
1) Mild chlorosis or necrosis appeared in water-seeded rice seedlings after the application of pyrazolate, but subsequently the symptoms did not affect the growth. Phytotoxicity including inhibition of shoot elongation and tillering of rice seedlings appeared after the application of bensulfuron-methyl·dimepiperate, pyrazosulfuron-ethyl·etobenzanid and imazosulfuron·etobenzanid·dymron. The degree of inhibition was different depending on the sowing depth of rice and the types of herbicides applied. Phytotoxicity was more severe in the seedlings sown at 0cm depth than in those at 1cm depth.
2) Inhibition of elongation of crown roots in the root system, which was considered to occur after the application of sulfonylurea herbicides, was observed after the application of bensulfuron-methyl·dimepiperate, pyrazosulfuron-ethyl·etobenzanid and imazo·sulfuron·etobenzanid·dymron. The degree of inhibition was larger for the seedlings sown at 0cm depth than for those at 1cm depth. Severe impairment of crown root elongation resulted in floating or inverted seedlings when the sowing depth was 0cm.
3) Decrease of dry weight was not observed in the seedlings sown at 1cm depth except after pyrazosulfuron-ethyl·etobenzanid application, but was observed in the seedlings sown at 0cm depth and the degree was different depending on the types of herbicides applied.