Effects of different concentrations (1, 2 and 5% v/w) of diesel and kerosene on N mineralization were studied in a sandy loam soil. Relative to the untreated soil, higher ammonium-N levels were obtained in samples treated with all the concentrations of kerosene and diesel from the second and third weeks of incubation respectively while extents of nitrate-N production differed. Net N-mineralization was 17.211 mg mineral-N/kg soil in untreated soil and -11.753 mg mineral-N/kg soil and -26.562 mg mineral-N/kg soil respectively in soils treated with 5% kerosene and diesel after six weeks incubation. Net nitrification was 29.90 mg NO3-N/kg soil in untreated soil and -9.35 mg NO3-N/kg soil and -22. NO3-N/kg soil respectively in soils treated with 5% kerosene and diesel after six weeks incubation. Overall mineralization rates were highest (13.01 mg N/kg soil per week) in untreated soil. Rates were lower in diesel than in kerosene treated soils. Inhibition of net N mineralisation ranged from of 139.31 to 168.29% and 90.41 to 254.34% after sixth week incubation for kerosene and diesel-treated soils respectively. The toxicity of diesel and kerosene treatment on nitrogen mineralization in the soil is due more to their effects on ammonium-N than on nitrate-N production.
Key words: Mineralisation, nitrification, ammonium, nitrate, diesel and kerosene.
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