Abstract
This experiment was conducted to clarify the effects of soil moisture on germination and emergence of seeds of upland weeds, grasses and common crops. The plants used in this experiment were large crab-grass (Digitaria adscendens Henr.), common lamb's quarters (Chenopodium album L.), Polygonum nodosum Pers., common purslane (Portulaca oleracea L.), Chufa (Cyperus microiria Steud.), livid amaranth (Amaranthus lividus L.), goose grass (Eleusine indica Gaertn.), Rhodes grass (Chloris gayana Kunth), green panic (Panicum maximum), upland rice (Oryza sativa L.), peanut (Arachis hypogaea L.), soybean (Glysine max (L.) Merill), corn (Zea mays L.), grain sorghum (Sorghum bicolor (L.) Moench) and African millet (Eleusine coracana (L.) Gaerth).
1) Seeds were setted in the soils having different soil moisture contents. Each plants showed the highest emergence percentage at the condition of 54.6% (pF 1.5) of soil moisture percentage on dried soil basis. Emergence percentage reduced and average length of time for emergence increased with decreased soil moisture percentage. The reduction of emergence percentage of weeds and grasses with decreased soil moisture percentage were more remarkable than that of common crops. The minimum soil moisture content allowing emergence of common crops was estimated about 20% of soil moisture percentage and that of weeds or grasses was estimated 25-30%. The difference of emergence with decreased soil moisture among weeds was not clear in this experiment.
2) The moisture absorbing power of seeds was related to the difference of emergence percentage with different soil moisture contents. Glucose was mixed with distilled water to obtain desired osmotic presseres, and seeds were germinated in water solutions having different osmotic presseres. From the results of this experiment, the moisture absorbing power of seeds was large in common crops and was small in weeds and grasses. The growth of plants was depressed at the condition of high osmotic presseres.
3) The soil moisture percentage of the surface of the ground (0-1cm) fell to 25-30% after several days of watering in the fields, and this was below the minimum soil moisture contents allowing emergence of weeds. But, soil moisture in lower layer (1-2cm) was relatively stable, so it was clear that a little difference in location of seeds was the important factor for emergence of seeds.
