Abstract
A self-propelled machine equipped with a steam chamber for weed seed disinfestation is being developed. The purposes of this paper were to determine 1) the effects of the steam treatment on seed mortality, 2) the relationship between seed burial depth and seed mortality, and 3) the relationship between seed moisture and seed mortality. We found 1) that the airtightness of the steam
chamber critically determined the heating effect; the mortality and dormancy break of weed seeds varied greatly depending on the
apparatus used. The maximum soil surface temperature was 95°C when the apparatus with the highest airtightness was used. Under these circumstances, seed mortalities of Ipomoea lacunosa L., Lolium multiflorum Lam., and Persicaria vulgaris Webb et Moq. were 88%, 46%, and 97%, respectively. Moreover, dormancy break was induced in I. lacunosa by soil surface temperature of 60 to 80°C using less airtight apparatus. 2) Steam application to the soil surface affected neither the temperature nor weed seed mortality in 5 cm depth. 3) Imbibed L. multiflorum seeds showed a significantly higher mortality (100%) than dry seeds. In conclusion, the control of steam leakage made it possible to increase soil temperature
rapidly and to kill weed seeds efficiently, despite the short heating duration compared with other thermal weed seed disinfestation methods.
