Carbon Dynamics in Corn-Soybean Sequences as Estimated from Natural Carbon-13 Abundance
1998
Huggins, D. R. | Clapp, C. E. | Allmaras, R. R. | Lamb, J. A. | Layese, M. F.
Carbon flow in terrestrial ecosystems regulates partitioning between soil organic C (SOC) and atmospheric CO₂. Our objectives were to assess SOC dynamics using natural ¹³C abundance in corn (Zea mays L., a C₄ species)-soybean [Glycine max (L.) Merr., a C₃ species] sequences. Fifteen treatments of continuous corn, continuous soybean, various sequences of corn and soybean, and fallow were initiated in 1981 at Lamberton, MN, on a Webster clay loam (fine-loamy, mixed, mesic Typic Haplaquoll). In 1991, soil and aboveground shoot samples from all treatments were analyzed for total organic C and δ¹³C. Carbon inputs, δ¹³C, and SOC were integrated into a two-pool model to evaluate C dynamics of corn and soybean. Total SOC was similar across all treatments after 10 yr; however, differences in soil δ¹³C occurred between continuous corn (δ¹³C = −17.2‰) and continuous soybean (δ¹³C = −18.2‰). Modeled C dynamics showed SOC decay rates of 0.011 yr⁻¹ for C₄-derived C and 0.007 yr⁻¹ for C₃-derived C, and humification rates of 0.16 yr⁻¹ for corn and 0.11 yr⁻¹ for soybean. Decay and humification rates were slightly lower than those found in other Corn Belt studies. Levels of SOC were predicted to decline an additional 7 to 18% with current C inputs from either corn or soybean, respectively. Annual C additions required for SOC maintenance averaged 5.6 Mg C ha⁻¹, 1.4 to 2.1 times greater than previously reported estimates. Controlled variation in natural ¹³C abundance in corn-soybean rotations during a 10-yr period adequately traced C dynamics. This paper is no. 971250024 of the Minnesota Agric. Exp. Stn. Journal Series.
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