Diuron mineralisation in a Mediterranean vineyard soil: impact of moisture content and temperature

BACKGROUND: The diuron‐mineralising ability of the microbiota of a Mediterranean vineyard soil exposed each year to this herbicide was measured. The impact of soil moisture and temperature on this microbial activity was assessed. RESULTS: The soil microbiota was shown to mineralise diuron. This mineralising activity was positively correlated with soil moisture content, being negligible at 5% and more than 30% at 20% soil moisture content. According to a double Gaussian model applied to fit the dataset, the optimum temperature/soil moisture conditions were 27.9 °C/19.3% for maximum mineralisation rate and 21.9 °C/18.3% for maximum percentage mineralisation. The impact of temperature and soil moisture content variations on diuron mineralisation was estimated. A simulated drought period had a suppressive effect on subsequent diuron mineralisation. This drought effect was more marked when higher temperatures were used to dry (40 °C versus 28 °C) or incubate (28 °C versus 20 °C) the soil. The diuron kinetic parameters measured after drought conditions were no longer in accordance with those estimated by the Gaussian model. CONCLUSION: Although soil microbiota can adapt to diuron mineralisation, its activity is strongly dependent on climatic conditions. It suggests that diuron is not rapidly degraded under Mediterranean climate, and that arable Mediterranean soils are likely to accumulate diuron residues. Copyright © 2010 Society of Chemical Industry     

Isoproturon mineralization in an agricultural soil

The impact of soil moisture content and temperature on isoproturon (3-(4-isopropylphenyl)-1,1-dimethyl-urea [IPU]) mineralization activity was assessed on an agricultural soil regularly exposed to this herbicide. Mineralization of ¹⁴C-IPU was monitored on soil microcosms incubated at different temperatures (10°C, 20°C, 28°C) and soil moisture contents (9%, 12%, 15, 18%, 21%, 24%). An increase in temperature and/or soil moisture significantly enhanced the maximum rate and percentage of IPU mineralization while it decreased the lag time before mineralization. The maximum rate and percentage of IPU mineralization respectively ranged from 0.18% day⁻¹ and 9% for the lowest temperature and soil moisture content pair (10°C–9%) to 1.51% day⁻¹ and 27.1% for the highest pair (28°C–24%). Statistics revealed a cross interaction of temperature and soil moisture content on the maximum rate of IPU mineralization. The optimum conditions for IPU mineralization, estimated from the double Gaussian model, were 25.8°C and 24% soil moisture content. The influence of fluctuations in soil moisture content on IPU-mineralization was investigated by subjecting the soil microcosms to drought stress. When IPU was added at the end of the drought stress, it had no statistical effect on IPU mineralization. However, when it was added before the drought stress, two mineralization phases were observed: (1) one corresponding to the drought stress for which mineralization was low and (2) another one observed after restoration of soil moisture content characterized by higher mineralization rate. It can be concluded that climatic fluctuations affect the activity of IPU mineralizing microbial community, and may lead to an increase in IPU persistence.