Urea hydrolysis and nitrogen transformations in soils containing different lead contents

Abstract

A laboratory experiment was carried out to study the urea hydrolysis and N-transformations in soil containing different lead (Pb) contents. Various Pb levels ranging from 52.1 – 589.9 mg kg−1 were created by mixing uncontaminated (containing 52.1 mg Pb kg−1 soil) and contaminated (containing 589.9 mg Pb kg−1 soil) soils in different proportions. Microbial biomass and urease activity declined with increasing levels of Pb in soil. Urea hydrolysis was faster in uncontaminated soil (97.2% within 24 h) compared to contaminated soil (91.1% within 24 h). Urea hydrolysis followed first-order kinetics, and the rate of hydrolysis reduced with an increase in Pb content of soil. The NH4 +-N content increased up to 1st day of incubation in soil containing Pb ⩽ 361.0 mg kg−1 and declined thereafter. Maximum accumulation of NH4 +-N was found on 7th and 14th day in the soils containing 496.4 and 589.9 mg Pb kg−1, respectively. The amount of NO3 −-N enhanced with incubation period and the maximum nitrification was observed between the 7th and 14th day.