Effect of summer flooding conditions on the seed viability of naturalized weeds, Camelina microcarpa Andrz. ex DC., Descurainia sophia (L.) Webb ex Prantl and Thlaspi arvense L.

Abstract

In Nagano Prefecture farms where wheat is repeatedly cultivated, the frequent occurrence of naturalized Brassicaceous weeds, Camelina microcarpa Andrz.ex DC., Descurainia sophia (L.) Webb ex Prantl and Thlaspi arvense L., caused some farmers to abandon growing wheat. To establish a cultural weed control method during the summer immediately after the wheat crop, we examined the influence that farm management practices have on seed survival of the three weed species.
Under normal field conditions, most seeds of the three weed species were completely viable. In two-month trials of farms undergoing a rotation from flooded to dry field conditions, the percentage of germinated weed seeds varied from 0 to 90% depending on the annual soil moisture conditions.
In paddy fields, germination of the three weed species decreased to around 10% and less than 1% with 1 and 2 months flooding, respectively.
In the fields converted from paddy fields that Thlaspi arvense L. tended to dominate, the soil seedbank decreased to about 5,400 seeds/m^-2 after conversion to paddy field cropping from 90,000/m^-2 before planting. However, after converting paddy fields back to wheat farming, the weed plant density returned to 75/m^-2, corresponding to a high infestation level.
In summary, summer flooding effectively suppressed the three weed species; however, to effectively suppress weed outbreaks in heavily infested fields at least two successive conversions of upland fields into paddy fields are necessary.