Abstract:
As heavy metals can persist in the soil for tens of thousands of years, the long-term effect of these
elements on soil productivity is a matter of intensively discussed. Soil microbial functions such as
respiration, carbon and nitrogen mineralization, biological nitrogen fixation etc., can thus be used
for monitoring heavy metal pollution. This experiment was conducted to evaluate the effect of
heavy metals on nitrogen mineralization and ntrification of agricultural soils. Soil in farm field at
faculty of Agriculture, amended with 10 umol/g of Cd, Cr, Zn and Pb separately. Soil without
contaminated by heavy metals served as the control treatments. Nitrogen mineralization and
nitrification were determined at 3, 7, 14, 21, 28, 42 and 56 days after incubation using Completely
Randomized Design (CRD) with four replicates. The results showed that heavy metals subject to
depressed both N mineralization and nitrification. At the beginning, N mineralization of the Cd,
Cr, Pb, Zn and control was 11.21, 14.98, 16.12, 15.87 and 29.87 mg/Kg of soils. Then at the end
of the incubation period N mineralization of the above treated samples deducted up to 2.36, 3.12,
6.15, 5.77 and 9.32 mg/Kg of soils respectively. The cumulative N mineralization of Cd, Cr, Pb
and Zn were 49.86, 59.93, 73.16, 71.66 and control was 111.5 mg/Kg of soils at the completion of
the testing period. The nitrification of the Cd, Cr, Pb , Zn and control was 19.90, 24.79, 30.11,
27.38 and 32.39 mg/Kg of soils at three days after incubation and at the completion of the
incubation values got as 1.20, 2.18, 2.54, 2.19 mg/Kg of soils for above respected treatments. The
cumulative nitrification was recorded as 86.84, 100.83, 114.02, 120.15 and 134.44 mg/Kg of soils
of Cd, Cr, Pb, Zn and control, respectively. Among the tested heavy metals Cd marked the highly
significant effect and Pb got the least significant on both N mineralization and nitrification
(P<0.05). According to the data it could be concluded, the heavy metals that make adverse effect
on nitrogen mineralization in soil and it depends on the type and toxicity of definite metal in the
soil.
