Physiological and Ecological Studies on Barnyard Grass (Echinocloa crus-galli BEAUV. var. oryzicola OHWI) : II. On the primary dormancy of the seed. (2) On the dormancy broken of the seed in the soil.

Abstract

The present report deals with the primary dormancy of seeds of barnyard grass in the soil, and the results are as follows: Under the room-temperature condition, the dormancy of the seeds were broken in a shorter period under storage in upland or submerged soil condition than on the dry or wet filter paper. The dormancy of the seeds stored in a paper bag at room temperature lasts about one year after harvest. The period of dormancy of seeds in the soil varied according to the temperature and moisture content of the soil. In the storage at lower temperature (3∼5°C) than germination temperature, process of the dormancy breaking progressed in all moisture content, and the speed of progress was faster at high moisture content. In the storage at optimum temperature for germination (20∼30°C), deep dormant seeds were awakened slowly in the air dry soil, but not awakened in submerged or upland soils untill about ten months after harvest. However, partially dormant seeds (no germination at germinator) were awakened from the dormancy rapidly by the storage in submerged soils, but were reinduced to dormancy by the storage in upland condition (soil moisture content 70 to 80 per cent of the field moisture capacity). Storage treatment in submerged soil was very effective to breaking the dormancy, if the seeds were already awakened from dormancy up to some degree by storage for 15 days or more at low temperature with wet condition. Optimum period and temperature for the storage treatment in submerged soil were varied with degree of dormancy. The shallower dormant seeds were awakened from dormancy with shorter period storage at various range of temperature (5°to 40°C), but in relatively deep dormant seeds the dormancy was broken after longer period storage at high temperature (30°C to 40°C). The cause of dormancy broken by storage treatment in submerged soil is the low oxygen content in the soil because the similar effects obtained from the storage treatment of seeds in nitrogen gas. Seeds that awakened from dormancy in the soils were reinduced to dormancy with air dry treatment. As the results of these findings, it was clarified that processes of the dormancy breaking were divided in five, and low temperature during from late autumn to early spring, alternating temperature in spring and submergence at the start of rice culture were important for breaking the primary dormancy of the seeds in paddy field.