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TECHNICAL REPORTS

Effect of Nitrogen Fertilizer Application on Growing Season Soil Carbon Dioxide Emission in a Corn–Soybean Rotation

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011-1010. M.L. Kruse, formerly graduate student

^* Corresponding author (malkaisi{at}iastate.edu).

Received for publication May 14, 2007. Nitrogen application can have a significant effect on soil carbon (C) pools, plant biomass production, and microbial biomass C processing. The focus of this study was to investigate the short-term effect of N fertilization on soil CO₂ emission and microbial biomass C. The study was conducted from 2001 to 2003 at four field sites in Iowa representing major soil associations and with a corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotation. The experimental design was a randomized complete block with four replications of four N rates (0, 90, 180, and 225 kg ha^–1). In the corn year, season-long cumulative soil CO₂ emission was greatest with the zero N application. There was no effect of N applied in the prior year on CO₂ emission in the soybean year, except at one of three sites, where greater applied N decreased CO₂ emission. Soil microbial biomass C (MBC) and net mineralization in soil collected during the corn year was not significantly increased with increase in N rate in two out of three sites. At all sites, soil CO₂ emission from aerobically incubated soil showed a more consistent declining trend with increase in N rate than found in the field. Nitrogen fertilization of corn reduced the soil CO₂ emission rate and seasonal cumulative loss in two out of three sites, and increased MBC at only one site with the highest N rate. Nitrogen application resulted in a reduction of both emission rate and season-long cumulative emission of CO₂–C from soil.

Abbreviations: CO₂, carbon dioxide • MBC, microbial biomass carbon • V6, sixth-leaf stage of corn