Simulating Soil Organic Carbon Dynamics with Residue Removal Using the CQESTR Model

Authors: Gollany, Hero; Novak, Jeffrey; LIANG, YI - Former ARS Employee; Albrecht, Stephan; RICKMAN, RON - Retired ARS Employee; Follett, Ronald; Wilhelm, Wallace; Hunt, Patrick

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2009
Publication Date: 1/8/2010
Citation: Gollany, H.T., Novak, J.M., Liang, Y., Albrecht, S.L., Rickman, R.W., Follett, R.F., Wilhelm, W.W., Hunt, P.G. 2010. Simulating Soil Organic Carbon Dynamics with Residue Removal Using the CQESTR Model. Soil Science Society of America Journal. 74:372-383

Interpretive Summary: Concerns about carbon dioxide emissions and fossil fuel supplies have increased interest in using crop residues for biofuel production; however, maintaining soil organic carbon through residue return is vital for maintaining soil productivity. We simulated long-term soil organic carbon changes of a loamy sand soil using the CQESTR model (a process-based carbon balance model), and examined the effect of tillage and residue harvest on soil organic carbon stocks. We used a long-term study in the mid Coastal Plain region of South Carolina to simulate four residue harvest rates over two harvest periods (1979-2002 and 1995-2014). Four residue removal scenarios used were: 1) 0%, no crop residue removed; 2) 50% of the crop residue removed; 3) 66% of the crop residue removed; and 4) 90% of the crop residue removed. We used CQESTR to predict soil organic carbon changes for two tillage practices, disking or conservation tillage using paratill. The CQESTR model performed well in capturing year–to¬–year variation of soil organic carbon. The predicted soil organic carbon stocks in the top 2 inches increased from 0.60 to 1.53% for this loamy sand soil, while measured values increased from 0.5 to 1.53%, during 23 years of conservation tillage. After 23years, simulated SOC stock gain was over threefold greater under conservation tillage than under disking. After 23 years of 66% residue removal, CQESTR predicted 21% and 30% reductions in soil organic carbon stocks in the top 2 inch depth under disking and paratill systems, respectively. The predicted soil organic carbon stocks under conservation tillage were about 0.5% greater than under DT, however, even with 90% residue harvest. Quantities of crop residue that can be sustainably harvested are directly influenced by initial soil organic carbon concentration and tillage practices. While conservation tillage can somewhat mitigate the loss of soil carbon, residue removal from soils in the mid Coastal Plain region may adversely affect soil organic carbon stocks. This in turn will have adverse implications for sustainable soil and water resources. Large-scale residue removal for bioenergy must be balanced with other critical functions that agricultural lands provide, including nutrient and water cycling, and carbon sequestration, for the maintenance of soil productivity.

Technical Abstract: Concerns about CO_2 emissions and fossil fuel supplies have enhanced interest in using crop residues for biofuel production; however, maintaining soil organic carbon (SOC) through residue return is vital for maintaining soil productivity. Our objectives were to simulate long-term SOC dynamics using CQESTR, and to examine the effect of residue harvest on SOC stocks under disking (DT) and conservation tillage (CS). A long-term study in the mid Coastal Plain region of South Carolina was used to simulate four residue harvest rates (0, 50, 66 and 90%) over two harvest periods. The yearly variation of SOC was predicted well (r^2 = 0.84, P < 0.0001). Without residue removal, average increases of 0.10 and 0.39 g SOC kg^-1 yr^-1 were predicted under DT and CS, respectively, consistent with observed increases of 0.12 and 0.44 g SOC kg^-1 yr^-1. After 23 yr, simulated SOC stock gain was over threefold greater under CS than DT (9.0 vs. 2.4 g SOC kg^-1). The model predicted 1.86 and 4.47 g SOC kg^-1 losses in the top 5 cm soil under DT and CS, respectively, during 23 yr of 66% residue harvest compared to no residue harvest. The predicted SOC stocks under CS were about 5 g SOC kg^-1 greater than under DT, however, even with 90% residue harvest. The quantities of crop residue that can be sustainably harvested were directly influenced by the initial SOC concentration and tillage practices. While CS can somewhat mitigate the loss of soil C, residue harvest from loamy sand soils may have an adverse impact on SOC stocks.