Restoring effect of soil acidity and Cu on N2O emissions from an acidic soil.

Heavy metals are believed to impact soil processes by influencing microbial communities, nutrient cycling or exchanging for essential plant nutrients. Soil pH adjustment highly influences the bio-availability of nutrients and microbial processes. We examined the effect of soil pH manipulation and copper (Cu as CuCl2.2H2O) application on nitrogen (N) cycling and nitrous oxide (N2O) emissions from an acid soil. Increasing amounts of Cu (0, 250, 500 and 1000 mg kg-1) were added to an acidic soil (pH = 5.44) that was further amended with increasing amounts of dolomite [CaMg(CO3)2] to increase soil pH. Dolomite increased soil pH values, which reached a maximum without Cu application (-Cu) at day 42 of the experiment. The soil pH values decreased with increasing dose of Cu, and remained low as compared with both control and dolomite amended soil. Ammonium (NH4+-N) concentrations were higher in Cu contaminated soil as compared with the control and dolomite treated soil. Nitrate (NO3--N) concentrations increased in dolomite treated soil when compared with the +Cu alone treatments and control. Microbial biomass carbon (MBC) and nitrogen (MBN) contents were higher in dolomite treated soil as compared with the +Cu treatments and control. The application of increasing amounts of Cu progressively decreased soil MBC and MBN. Nitrous oxide emissions were higher (p ≤ 0.01) in +Cu soil as compared with the control, and increased with increasing Cu concentration in soil. Application of dolomite highly suppressed soil N2O emissions in both +Cu and -Cu soils. The results indicate that the effects of heavy metal contamination (specifically Cu contamination) can increase N2O emissions, but this can be effectively mitigated through increasing soil pH, also decreasing potential toxic effects on soil microorganisms.