Effect of lead on the transformation of urea-N in fly ash-contaminated soils under different moisture regimes

Urea is applied to soil for plant growth and undergoes various changes while in the soil. The mobility of heavy metals changes with the transformation of urea applied to the soil that, in turn, affects the activity of microbial biomass. The objective of this study was to determine the interaction between lead (Pb) and urea under two moisture regimes (60% and saturated water contents). At 60% water content, the amount of NH4-N decreased with the incubation time, irrespective of Pb and urea applied, while the amount of NO3-N content in the soil gradually increased with the incubation period to 28 days, and such an increase was counteracted by application of Pb. The amount of NO3-N content was higher than that of NH4-N, however, under saturated moisture condition, the amount of NH4-N was increased with the incubation time regardless of the levels of Pb application. The amount of NO3-N content in the soil gradually decreased with the advance of incubation at saturated condition. Although application of urea increased the NO3-N content in the soil, such an increase was suppressed by the application of different levels of Pb at water saturated condition throughout the incubation period.