Abstract
Effects of six granular formulations of pesticides on ammonium oxidizing activity in a simulated oxidized layer of paddy soil were investigated. In simple comparison with untreated control, it was found that the activity was stimulated by Moncut®, Admire® and the field application dose of Coratop®, inhibited by Oryzemate®, Fuji-One® and the fivefold dose of Coratop® and not affected by Zark D®. However, the initial pHs of the paddy water added with some of the granules were higher than that of untreated control suggesting that the granules contain alkaline auxiliary substances which affect the activity. In comparison with the activity at the corresponding pH, it was found that the stimulations by Moncut® and Admire® were due wholly and partly to the alkaline auxiliary substance in themselves. Additionally, it was found that Coratop® and Zark D® contain the inhibitor of which the effects are undetectable and missed in the simple comparison. It is concluded that the net effect of pesticide can be under- or over-evaluated in simple comparison to untreated control only and that consideration on the change of pH in soil culture is indispensable, in the assessment of effect of pesticide on nitrification using formulated products.
