Annual carbon dioxide exchange in irrigated and rainfed maize-based agroecosystems

Authors

Shashi Verma, University of Nebraska-LincolnFollow
Achim Dobermann, University of Nebraska-Lincoln
Kenneth G. Cassman, University of Nebraska-LincolnFollow
Daniel T. Walters, University of Nebraska-LincolnFollow
Johannes M. H. Knops, University of Nebraska-LincolnFollow
Timothy J. Arkebauer, University of Nebraska-LincolnFollow
Andrew E. Suyker, University of Nebraska-LincolnFollow
George Burba, University of Nebraska-LincolnFollow
Brigid Amos, University of Nebraska-LincolnFollow
Haishun Yang, University of Nebraska-LincolnFollow
Daniel Ginting, University of Nebraska-LincolnFollow
Kenneth Hubbard, University of Nebraska-LincolnFollow
Anatoly A. Gitelson, University of Nebraska-LincolnFollow
Elizabeth A. Walter-Shea, University of Nebraska-LincolnFollow

Date of this Version

7-25-2005

Comments

Published in Agricultural and Forest Meteorology 131:1-2 (July 25, 2005), pp. 77–96; doi 10.1016/j.agrformet.2005.05.003 http://www.sciencedirect.com/science/journal/01681923 Copyright © 2005 Elsevier B.V. Used by permission.

Abstract

Carbon dioxide exchange was quantified in maize–soybean agroecosystems employing year-round tower eddy covariance flux systems and measurements of soil C stocks, CO₂ fluxes from the soil surface, plant biomass, and litter decomposition. Measurements were made in three cropping systems: (a) irrigated continuous maize, (b) irrigated maize–soybean rotation, and (c) rainfed maize–soybean rotation during 2001–2004. Because of a variable cropping history, all three sites were uniformly tilled by disking prior to initiation of the study. Since then, all sites are under no-till, and crop and soil management follow best management practices prescribed for production-scale systems. Cumulative daily gain of C by the crops (from planting to physiological maturity), determined from the measured eddy covariance CO₂ fluxes and estimated heterotrophic respiration, compared well with the measured total above and belowground biomass. Two contrasting features of maize and soybean CO₂ exchange are notable. The value of integrated GPP (gross primary productivity) for both irrigated and rainfed maize over the growing season was substantially larger (ca. 2:1 ratio) than that for soybean. Also, soybean lost a larger portion (0.80–0.85) of GPP as ecosystem respiration (due, in part, to the large amount of maize residue from the previous year), as compared to maize (0.55– 0.65). Therefore, the seasonally integrated NEP (net ecosystem production) in maize was larger by a 4:1 ratio (approximately), as compared to soybean. Enhanced soil moisture conditions in the irrigated maize and soybean fields caused an increase in ecosystem respiration, thus eliminating any advantage of increased GPP and giving about the same values for the growing season NEP as the rainfed fields. On an annual basis, the NEP of irrigated continuous maize was 517, 424, and 381 g C m^-2 year^-1 , respectively, during the 3 years of our study. In rainfed maize the annual NEP was 510 and 397 g C m^-2 year^-1 in years 1 and 3, respectively. The annual NEP in the irrigated and rainfed soybean fields were in the range of −18 to −48 g C m^-2. Accounting for the grain C removed during harvest and the CO₂ released from irrigation water, our tower eddy covariance flux data over the first 3 years suggest that, at this time: (a) the rainfed maize–soybean rotation system is C neutral, (b) the irrigated continuous maize is nearly C neutral or a slight source of C, and (c) the irrigated maize–soybean rotation is a moderate source of C. Direct measurement of soil C stocks could not detect a statistically significant change in soil organic carbon during the first 3 years of no-till farming in these three cropping systems.