Influence of flooding on the degradation of linuron, isoproturon and metolachlor in soil

Abstract - Degradation of pesticides in soil usually refers to normally aerated conditions. However, considering that under some circumstances, fields treated with pesticide can be subject to flooding phenomena, more information on pesticide persistence under these conditions is needed. The main objective of the present study was to investigate the persistence of linuron, isoproturon and metolachlor in soil samples incubated under flooding conditions. During the whole incubation period, changes in soil Eh, pH and microbial C were measured. Flooding conditions produced different effects on the persistence of the three herbicides. More specifically, flooding conditions led to a significant increase in linuron and isoproturon persistence. The half-lives of linuron and isoproturon in flooded soil were 1.8 and 1.4 times higher than in nonflooded soil, respectively. An opposite phenomenon was observed with metolachlor. The half-life of metolachlor was reduced from 32.2 to 24.1 days in nonflooded and flooded soil, respectively. Soil Eh rapidly decreased in soil samples incubated under flooding conditions, passing form 368.0 mV to - 225.5 mV within the first week of flooding. No significant changes in soil microbial C in soil samples incubated under the two water regimes were observed. The results obtained from the present experiment showed that information from normally aerated soil conditions is not correctly applicable to predict herbicide persistence under flooding conditions.