Studies of the Effect of Root-cutting Treatment on Growth and Yield in Direct Sowing Culture of Paddy Rice : I. Changes in the morphological and ecological characteristics caused by root-cutting treatment and the relationship to growth behavior

Abstract

For stable and high-yielding rice cultivation by direct sowing method, it is necessary to develop new technology for growth control of rice plants which can make up for defects peculiar to the direct sowing culture. As one of the promising methods for the above purpose, root-cutting treatment on rice plants at the early growth stage has been regarded effective. In the present paper the root-cutting treatment is dealt in the light of morphology and ecology of rice plants. The direct sown plants were grown under upland field condition and rice roots were cut 40-45 days after sowing, and afterward paddy soil was irrigated. Cutting of roots was done on both sides or one side at an angle of 20°-40° to the ground surface. The result are summarized as follows: 1. Roots cutting treatment decreased water absorption and transpiration and brought about so severe water stress on the plant that wilting of leaves lasted for about ten days. 2. As to the relationship between the time of root-cutting treatment and that of tiller bud emergence, the treatment after shooting of tiller bud from the main culm did not have any growth control effect on the plant, whereas the treatment before tiller bud can be recognized checked tillering. Root-cutting after the tiller bud was observed retarded the emergence of the secondary tiller. Intensive root-cutting treatment affected roots development, stimulating new thick roots to grow, while slight root-cutting treatment increased branched roots to shoot vigorously out of the old remaining roots. 3. The root-cutting treatment shortened the lower(4th) internode of the plant and thickened culm wall, consequently contributing to the increase of breaking strength and lodging resistance of the plant. 4. Besides such advantageous effect of root-cutting treatment as control of luxuriant plant growth and excessive tillering, the experiment demonstrated that the plant-type was improved to be erect and especially the angle of foliage leaf to main stem axis was decreased which are an important character for rice plants to intercept sunlight sufficient for dry matter production. 5. In the root-cutting experiment, increase of the number of stomatal cells in the upper leaves and decrease of their size were observed at the ripening stage. Such changes suggest that hardening of the plant developed. The phenomenon is considered as an after-effect of water stress to root-cutting.