Emission of greenhouse gases from an agricultural soil amended with urea: A laboratory study

Urea is the most used N fertilizer in the world, but its effect on emissions of greenhouse gases (GHG), i.e. carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4), from agricultural soil of central Mexico remains largely unstudied. An agricultural soil was conditioned or not for 7 days,amended with or without 200 mg urea-N kg(-1) soil and incubated aerobically with or without acetylene (C2H2), while dynamics of mineral N and emissions of CO2, N2O and CH4 were monitored. The emission of CO2 increased when urea was added to the soil, but C2H2 did not affect it. Application of C2H2 to soil amended with or without urea decreased the emission of N2O >10 times. Emissions of CH4 were low, i.e. <260 ng kg(-1) day(-1), and not affected by C2H2 or urea in the unconditioned soil. Hydrolysis of urea occurred within the first day, but oxidation of ammonium (NH4*) and increases in the concentrations of nitrate (NO3-) were limited after 7 days. It was found that application of urea and wetting the soil increased microbial activity as evidenced by emissions of CO2, but C2H2 had no effect on it. Application of urea and wetting the soil also increased the emission of N2O, while C2H2 inhibited it. Emissions of CH4 were small, and urea, wetting the soil and C2H2 had little effect on it. As such, short time changes in soil water content and application of urea increased GHG emissions. (c) 2010 Elsevier B.V. All rights reserved.