Free-air Carbon Dioxide Enrichment of Wheat: Soil Carbon and Nitrogen Dynamics
1997
Prior, Stephen A. | Torbert, H. Allen | Runion, G. B. | Rogers, H. H. | Wood, C. W. | Kimball, B. A. | LaMorte, R. L. | Pinter, P. J. | Wall, G. W.
The predicted positive impact of elevated atmospheric carbon dioxide (CO₂) concentration on crop biomass production suggests that more C will reach the soil. An aspect of soil C sequestration that requires further study is the effect of elevated CO₂ on C and N dynamics; this relationship is the key to understanding potential long-term C storage in soil. Soil samples (0–5, 5–10, and 10–20 cm increments) were collected after 2 yr of wheat (Triticum aestirum L.) production under two CO₂ levels [370 (ambient) and 550 µL L⁻¹ (free-air CO₂ enrichment)(FACE)] and two water treatments [100% of ET replaced (wet) and 50% of ET replaced (dry)] on a Trix clay loam [fine, loamy, mixed (calcareous), hyperthermic Typic Torrifluvents] at Maricopa, AZ. Organic C, total N, potential C and N mineralization, and C turnover were determined during a 60-d incubation study. Organic C content increased at all three soil depths under FACE and the total N content increased at the 5 to 10 and 10 to 20 cm depths. In general, increased N mineralization under dry conditions corresponded well with patterns of higher C mineralization and turnover. Nitrogen mineralization was unaffected by CO₂ treatment, indicating that factors other than N may limit C mineralization and turnover. Soil respiration and C turnover patterns were not affected by CO₂ treatment level at the 0 to 5 cm depth; however, these measures were lower under FACE at the lower depths. Soil respiration and C turnover at the 10 to 20 cm depth were increased by water stress under ambient CO₂; these measures under both water levels for FACE were similar to the ambient CO₂/wet treatment, suggesting that more C storage in wheat cropping systems is likely under elevated CO₂ regardless of water treatment.
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