Crop rotation and nitrogen fertilization effect on soil CO 2 emissions in central Iowa H.M. Wilson a , M.M. Al-Kaisi b, * a Department of Ecology, Evolutionary, and Organismal Biology, 253 Bessey Hall, Iowa State University, Ames, IA 50011-1020, United States b Department of Agronomy, 2104 Agronomy Hall, Iowa State University, Ames, IA 50011-1010, United States 1. Introduction Soil is the largest reservoir of terrestrial carbon (C) storing approximately 53% of the terrestrial C (Lal, 2004). The atmospheric carbon dioxide (CO 2 ) concentration has increased about 85 ppm in the last 100 years (Lal, 2004) and approxi- mately 10% of the CO 2 in the atmosphere passes through the soil each year (Raich and Potter, 1995). The increase in atmospheric CO 2 concentration has increased the effort that is being devoted to explore the potential of agricultural land to sequester C. Several soil management practices influence the potential of agricultural soil to be utilized as a sink of CO 2 . Nitrogen fertilization and crop rotation may play a significant role in impacting soil C (Lal, 2004). Nitrogen fertilization impacts the soil C pool in two ways. One, increasing N fertilization will increase crop biomass in several crops and two, N availability is critical for the microbial decomposition of crop residue (Green et al., 1995). Limited information is available regarding the effects of N fertilization on in situ soil CO 2 emissions from agricultural applied soil ecology 39 (2008) 264–270 article info Article history: Received 31 July 2006 Received in revised form 12 December 2007 Accepted 21 December 2007 Keywords: Soil C CO 2 C input Microbial biomass abstract Depending upon how soil is managed, it can serve as a source or sink for atmospheric carbon dioxide (CO 2 ). As the atmospheric CO 2 concentration continues to increase, more attention is being focused on the soil as a possible sink for atmospheric CO 2 . This study was conducted to examine the short-term effects of crop rotation and N fertilization on soil CO 2 emissions in Central Iowa. Soil CO 2 emissions were measured during the growing seasons of 2003 and 2004 from plots fertilized with three N rates (0, 135, and 270 kg N ha 1 ) in continuous corn and a corn–soybean rotation in a split-plot design. Soil samples were collected in the spring of 2004 from the 0–15 cm soil depth to determine soil organic C content. Crop residue input was estimated using a harvest index based on the measured crop yield. The results show that increasing N fertilization generally decreased soil CO 2 emissions and the continuous corn cropping system had higher soil CO 2 emissions than the corn–soybean rotation. Soil CO 2 emission rate at the peak time during the growing season and cumulative CO 2 under con- tinuous corn increased by 24 and 18%, respectively compared to that from corn–soybean rotation. During this period, the soil fertilized with 270 kg N ha 1 emitted, on average, 23% less CO 2 than the soil fertilized with the other two N rates. The greatest difference in CO 2 emission rate was observed in 2004; where plots that received 0 N rate had 31% greater CO 2 emission rate than plots fertilized with 270 kg N ha 1 . The findings of this research indicate that changes in cropping systems can have immediate impact on both rate and cumulative soil CO 2 emissions, where continuous corn caused greater soil CO 2 emissions than corn soybean rotation. # 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +1 515 294 8304; fax: +1 515 294 9985. E-mail address: malkaisi@iastate.edu (M.M. Al-Kaisi). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/apsoil 0929-1393/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsoil.2007.12.013