See more from this Session: General Soil and Environmental Quality Posters: I
Tuesday, October 18, 2011
Henry Gonzalez Convention Center, Hall C, Street Level
Legume rotations and animal manures can reduce synthetic fertilizer use but may affect emissions of greenhouse gases and ammonia in a row cropping. In 2006-2007, soil-atmosphere fluxes of N2O, NH3, and CO2 were measured in maize (Zea mays L.) crops within a replicated long-term experiment comparing continuous maize to maize–alfalfa (Medicago sativa L.) rotations. In both systems, comparisons of synthetic fertilizer N and manure N were initiated in 1990. With inorganic fertilizer as the main N source, mean CO2–C fluxes were lower from continuous maize (CC, 512 ± 132 g m–2 growing season–1) than from maize following alfalfa (CA, 691 ± 91 g m–2 growing season–1). In contrast, with manure as the main N source, mean soil CO2–C fluxes from CC (943 ± 111 g m–2 growing season–1) were greater than from CA (682 ± 21 g m–2 growing season–1). Soil CO2–C emissions correlated with long-term inputs of manure. Synthetically fertilized continuous maize had lower N2O-N fluxes (0.36 ± 0.26 g m–2 growing season–1) than other treatments (0.55–0.58 g m–2 growing season–1). Nitrous oxide-N fluxes were not correlated with current N inputs or soil nitrate concentrations, suggesting that long-term treatment effects (e.g., on soil structure, labile C, or microbial communities) contribute to contemporary N2O variation. Elevated NH3 fluxes (>5 mg NH3–N m–2 h–1) followed manure applications, but within weeks there were no significant treatment differences in NH3 fluxes. This study shows that short-term or single-factor experiment may not capture important interactions among crop rotations and N sources affecting greenhouse gas emissions from agricultural soils.