Soil moisture and the rates of biodegradation of diallate and triallate

Abstract

Degradation experiments were combined with biomass measurements and adsorption tests to determine how soil moisture content influences the rates of degradation of 41C-labelled diallate and triallate. In soils treated with 1 μg −1 herbicide and incubated at constant temperature and moisture, degradation rates were regulated by two variables: the quantity of microbial biomass in the soil; and the quantity of herbicide dissolved in the soil solution. The quantity of biomass was influenced by soil water content and the duration of incubation. The amounts of herbicide in solution were determined by the amount of water present and the total quantity of herbicide in the soil. In all soil samples, the rates of degradation increased with increasing water content but decreased with prolonged incubation. The factors responsible for decrease with time were the loss of biomass during incubation and the decline in herbicide concentration in the soils as degradation proceeded.