Abstract
The noxious weeds in winter cropping on drained paddy fields in Japan are Alopecurus aequalis, Beckmannia erucaeformis, Agropyrum semicostatum, Poa annua, Stellaria uliginosa, S. media, Sagina japonica, Cardamine flexuosa, Galium Aparine and Lapsna apogonoides, and their ecological characteristics, such as dormancy, germination, emergence and longevity of seeds in the soil, are as follows. 1. Freshly harvested ripened seeds of these weeds are more or less dormant (Fig. 1), and the dormancy of them is overcome by autumn in soil outdoors (Fig. 2). Low-temperature treatment (5°C, moist) is effective to overcome the dormancy for 4 species belonging to Gramineae (Fig. 3). The dormancy of most species is overcome by placing the seeds at high temperature (30°C) in moist condition (high-temperature treatment) in normal air or in absence of oxygen for some periods (Fig. 4). 2. Though optimum temperature for germination vary more or less according to kinds, it is generally from 10°or 15°to 20°C. The germination of all kinds of seeds except Alopecurus aequalis is favored by light (Fig. 5). Some seeds do not germinate and others germinate to a lesser degree under the continuous dark condition. No germination occurs in absence of oxygen, and oxygen requirement for germination is not same for each weed (Fig. 6). 3. The maximum elongation length of plumule in a dark germinator varies according to kinds and is correlated with seed size in general. Depth of emergence is generally shallow, but differs with weed kinds (Tab. 1). It is caused by differences of weeds in light requirement for germination and in penetrating power of plumule through the soil layers as well as in the maximum elongation length of plumule in the dark condition. 4. Longevity of seeds in the soil of paddy fields (upland fields condition from autumn to spring) or upland fields is generally short, but it varies from one to two years according to the kind of weeds and moisture content of soil. The longevity of seeds is closely related to the germinating ability within soils. 5. The above-mentioned facts show that these weeds vary in main ecological characteristics in detail each other, though they are adapted to the environmental conditions of winter cropping on drained paddy fields.
