Soil greenhouse gas and ammonia emissions in long-term maize-based cropping systems.

摘要

Legume rotations and animal manures can reduce synthetic fertilizer use in row crops, but only long-term experiments can elucidate effects of multiple legume rotations and decades of manure additions on soil gas emissions. In 2006 and 2007, we measured soil-atmosphere fluxes of N₂O, NH₃, and CO₂ in maize (Zea mays L.) crops within a replicated experiment comparing continuous maize to maize-alfalfa (Medicago sativa L.) rotations initiated in 1969. In both systems, comparisons of synthetic fertilizer N and manure N were initiated in 1990. With synthetic fertilizer as the main N source, mean CO₂-C fluxes (from March 31st to October18th) were lower from continuous maize (CC, 512+or-132 g m-2 growing season-1) than from maize following alfalfa (CA, 691+or-91 g m-2 growing season-1). In contrast, with manure as the main N source, mean soil CO₂-C fluxes from CC (943+or-111 g m-2 growing season-1) were greater than from CA (682+or-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+or-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. These results suggest that short-term or single-factor studies may not capture important interactions among crop rotations and N sources affecting greenhouse gas emissions from agricultural soils.