Effect of Nitrogen Source on CH4 Emissions from Grassland Soil

Methane (CH₄) is an important greenhouse gas. Its global warming potential is ~32 times higher than carbon dioxide (CO₂). Animal feces is the main source of CH₄ in grassland sites. It has been speculated that methanogenic and methanotrophic microorganism activity can be affected by nitrogen source and consequently CH₄ fluxes. The aim of this study was to analyze the effect of different sources of nitrogen applied to a grassland soil on CH₄ fluxes. The experimental design was completely randomized with 3 treatments and 4 replicates. The treatments were three sources of nitrogen (ammonium, nitrate and urea) applied to the soil using urea, potassium nitrate and ammonium sulfate. An incubation under controlled conditions was carried out to quantify the CH₄ fluxes from a tropical Ferralsol. The CH₄ emissions were evaluated using static closed chamber and the gas concentration was determined by gas chromatography. The ANOVA was performed using the cumulative CH₄ emissions that were obtained integrating the fluxes over time. Tukey test was run to distinguish differences among means. The cumulative CH₄ production was -1.19 (0.24), -1.26 (0.09) and 0.88 (0.84) mg CH₄.m^-2 for ammonium, nitrate and urea, respectively. The sources of nitrogen tended to influence the CH₄ emissions (P < 0.1). The treatment urea induced CH₄ emission while for the sources ammonium and nitrate, CH₄ was oxidized. These differences can be attributed to the molecular composition of N sources. The CO₂ produced during urea hydrolysis can be converted to CH₄ and this probably explains the CH₄ emissions at ~2.4 times higher for urea compared to the ammonium sulfate and potassium nitrate. In a tropical grassland, CH₄ emission or oxidation vary according to the nitrogen source applied to the soil.