This study was conducted under laboratory conditions to investigate the effect of different concentrations of oxyfluorfen herbicide on the numbers and diversity of the main groups of soil microflora in two soil types. The numbers of microorganisms in oxyfluorfen treated soils were determined at zero time and then at 15 days interval for 45 days. Oxyfluorfen residue in soils was determined by Gas Liquid Chromatography (GLC). Results showed that the numbers of organic nitrogen users were inhibited at 15 days with maximum inhibition percentage (65.2%) observed in Elsilait soil treated with 4000 mg kg-1. The highest increment percentage (97.8%) was observed in Gerif soil sample treated with 400 mg kg-1 after 30 days. Maximum inhibition percentage in inorganic nitrogen users was 42.4% which was recorded for soil treated with 96 mg kg-1 herbicide. Numbers of Mycobacterium spp. which were absolutely dominant in the nitrate agar medium decreased as from the beginning of the incubation period up to 45 days. The highest increment percent (180.1%) in fungal population was observed in Elsilait soil treated with 4000 mg kg-1. At low concentrations of the herbicide, degradation started after 15 days of incubation while at higher levels, a noticeable degradation was observed after 30 days of incubation in Elsilait loam soil. In Gerif silt loam soil the degradation percentages of the herbicide were generally very low at all concentrations tested compared to those observed in Elsilait loam soil. It could be concluded that the effect of oxyfluorfen on soil microorganisms depends on the group of microorganisms and soil type. While the growth of fungi, organic and inorganic nitrogen users, is enhanced, at least in low oxyfluorfen concentrations, the growth of Mycobacterium was inhibited at all concentrations tested. Higher degradation percentages were recorded in Elsilait soil (55.2-78.3%) compared to Gerif soil (6.0-9.5%).
Adil A. El Hussein, Afrah T. Mohamed, Marmar A. El Siddig, Ashraf M. Sherif and Awad G. Osman, 2012. Effects of Oxyfluorfen Herbicide on Microorganisms in Loam and Silt Loam Soils. Research Journal of Environmental Sciences, 6: 134-145.