Vol. 16—1962 - NorthEastern Weed Science Society

In another experiment, loam soil was treated with amiben
(at 0.25, 0.5, 1, 2, 4 or 6 lb/A) at 5 week intervals for a total
of 7 applioations. Oats were planted in the soil after each
application. In general, the first herbicid~ application resulted
in the greatest yield decrease relative to the check. Further
amiben applications produced a lower constant yield depression at
all rates. Therefore, it seemeQ that there was little build up of
herbicide toxicity. Since leaching from the containers was
impossible and volatilization was unlikely, the loss of herbicide
(lack of accumulation) would seem to be due to either chemical or
micro-organism breakdown. In experiments designed to separate
these possibilities, it was tound that loss otam1ben toxicity
from incubated soil was more rapid in muck than in clay. There
was no detoxification in sandy soil during the 10 week period indicating
that microbial breakdown of amiben is negligible in this
type ot soil.
When the two factors leaching and microbial detoxification
are considered, it would appear that leaching is the major
factor in amiben disappearance trom sand. Loss of actiVity from
muck and clay soils is dependent on both leaching and microorganism
activity, with the latter probably being more important
in muck. OUtdoor incubation of muck and clay soils showed that
considerable breakdown could occur during the cropping season.
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