Digitaria ciliarisseed banks in untilled and tilled soybean fields.

We gained an understanding of the vertical distribution and seasonal dynamics ofDigitaria ciliaris(Retz.) Koeler seed banks in untilled and tilled soybean fields using studies on naturally established seed banks and on seeds stored in the field. In untilled fields,D. ciliarisseeds were highly concentrated on or near the soil surface from late autumn to spring, whereas only a few seeds were found on the soil surface in the following summer. One year after tillage, there was a high concentration of the seeds on the soil surface. In the tilled fields, seeds were distributed uniformly throughout the soil profile and were present all year long, with only a few seeds found in the following summer. A study of seeds that were artificially buried or stored on the soil surface verified thatD. ciliarisseeds were extremely short-lived in the field and could not form a large, persistent seed bank, even when the seeds were buried by tillage. Tillage contributes to suppression ofD. ciliarisseedling emergence by reducing the number of seeds that are on or near the soil surface. Furthermore,D. ciliarisseeds showed a greater need for light in order to germinate throughout the year, even when they were stored on the soil surface. Particularly, light was critical for germination during summer. The light requirement for germination should be one reason why viableD. ciliarisseeds on the soil surface are carried over into the next season in untilled fields. [ABSTRACT FROM AUTHOR]