Studies on Ecological Changes and Control of Weeds in Upland Irrigation Culture

III. Effect of Soil Moisture on Dormancy Breaking of Seeds of Principal Annual Weeds on Upland Fields

Abstract

Dormancy breaking of seeds of principal twelve species of annual weeds on upland fields were investigated under four soil moisture levels of 43%, 63%, 85% of the maximum water holding capacity and flooding.
1. Seed dormancy of Alopecurus aequalis var. amurensis, Stellaria uliginosa var. undulata and Capsella Bursa-pastoris was broken earlier under the 85% soil moisture level. That of Poa annua and Cerastium caespitosum var. ianthes was broken almost at the same time under each soil moisture condition.
Under the flooded condition few seeds of weeds except Alopecurus aequalis var. amurensis emerged. The seeds of Cerastium caespitosum var. ianthes and Capsella Bursa-pastoris not emerged were estimated to be almost dead.
2. The dormancy breaking of Polygonum Blumei was delayed under the flooded condition. That of Polygonum Persicaria was promoted in accordance with the increase of soil moisture level except for the flooded condition.
3. The dormancy breaking of Digitaria adscendens and Eleusine indica was delayed under the flooded condition, but the seeds were still viable. That of Portulaca oleracea and Cyperus iria was little different among each soil moisture level.
In the case of Amaranthus viridis was delayed a little under the 85% soil moisture.
It seemed that most seeds of P. oleracea, A. viridis and C. iria died under the flooded condition during the period from the middle of October to the middle of April.