Mathematical descriptions of accelerated transformation of 1,3-dichloropropene in soil; a microbiological assessment

The rate of transformation of the soil fumigant (Z)-and (E)-1,3-dichloropropene in moist soil layers was measured at incubation temperatures of 5 degrees C, 10 degrees C and 20 degrees C. 'DD95' was added to four characterized soil layers, in amounts corresponding to realistic field contents after fumigation. Rapid transformation immediately after application was observed in layers with low initial contents (30-300 micrograms/kg dm) and could well be described with a first-order rate model. Incubation at higher doses (5-15 mg/kg dm respectively) showed distinctly different transformation pathways. Degradation curves could well be computed using a microbiological interspective competition (MIC) model for moist soil. The transformation rate is inversely correlated to microorganism population size and growth. Transformation curves described by MIC are characterized by a lag-time, a period of accelerated transformation and a period of decreasing transformation rates. At low temperatures, DT50 values of more than 20 days could be observed. First-order rate computations did not exceed 8 days. The use of different mathematical discriptions for various soil layers and soil temperatures permits simulation of DD95-transformation by microorganisms in the soil profile throughout the growing season.