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

Abstract

Urea is the most used N fertilizer in the world, but its effect on emissions of greenhouse gases (GHG), i.e. carbon dioxide (CO 2), nitrous oxide (N 2O) and methane (CH 4), 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 (C 2H 2), while dynamics of mineral N and emissions of CO 2, N 2O and CH 4 were monitored. The emission of CO 2 increased when urea was added to the soil, but C 2H 2 did not affect it. Application of C 2H 2 to soil amended with or without urea decreased the emission of N 2O >10 times. Emissions of CH 4 were low, i.e. <260 ng kg −1 day −1, and not affected by C 2H 2 or urea in the unconditioned soil. Hydrolysis of urea occurred within the first day, but oxidation of ammonium (NH 4 +) and increases in the concentrations of nitrate (NO 3 −) were limited after 7 days. It was found that application of urea and wetting the soil increased microbial activity as evidenced by emissions of CO 2, but C 2H 2 had no effect on it. Application of urea and wetting the soil also increased the emission of N 2O, while C 2H 2 inhibited it. Emissions of CH 4 were small, and urea, wetting the soil and C 2H 2 had little effect on it. As such, short time changes in soil water content and application of urea increased GHG emissions.