SOIL CONSERVATION SYSTEMS FOR SUSTAINABILITY OF PACIFIC NORTHWEST AGRICULTURE
Location: Soil and Water Conservation Research
Title: Simulating Soil Organic Matter Dynamics and Effects of Residue Removal Using the CQESTR Model
Submitted to: International Symposium on Soil Organic Matter Dynamics: Land Use, Management and Global Change
Publication Type: Proceedings
Publication Acceptance Date: April 29, 2009
Publication Date: July 1, 2009
Citation: Gollany, H.T., Rickman, R.W., Novak, J.M., Liang, Y., Albrecht, S.L., Follett, R.F., Wilhelm, W.W., Hunt, P.G. 2009. Simulating Soil Organic Matter Dynamics and Effects of Residue Removal Using the CQESTR Model. Conference Proceeding of International Symposium on Soil Organic Matter Dynamics: Land Use, Management and Global Change. July 6-9, 2009. P.43.
Concern about CO2 emissions and fossil fuel supplies has increased interest in using crop residues for biofuel production. However, maintaining soil organic matter (SOM) is vital for maintaining soil productivity. Our objectives were to simulate long-term SOM dynamics of a sandy loam soil using the CQESTR model, and examine the effect of tillage and residue harvest on SOM content. A long-term tillage and crop management study was initiated in 1979 at the Clemson University Pee Dee Research and Education Center on a Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudult) of the Mid Coastal Plain region of South Carolina. Four residue harvest scenarios (H0, H50, H66, and H90, representing conditions where 0%, 50%, 66% and 90% of the crop biomass was harvested) were implemented at two harvest stages: SP, 1979- 2002; and SF, 1995-2014. The model was used to simulate SOM dynamics under two tillage practices, disking (DT) and conservation tillage (CS) using paratill. Results were compared with measured values. CQESTR captured year to year variation in SOM content well. Without residue removal, average increases of 0.18 and 0.66 g SOM kg/yr were predicted for DT and CS, respectively. The increase in SOM was attributed to change in crop rotation and improved management practices. Higher SOM stocks under CS than under DT were due to lower OM mineralization rate with less tillage. CQESTR predicted 3.2 and 7.7 g SOM/kg losses in the top 5-cm under DT and CS during 23-yr of 66% residue harvest (H66), respectively. Losses of 10.6 and 7.0 g SOM/kg in the top 5-cm were predicted for CS under the SP-H90 and SF-H90 harvest simulation scenarios, respectively. The predicted loss of 10.6 g SOM/kg in the 0- to 5-cm depth is 70% of the amount of SOM gained (15.1 g SOM/kg) after implementing CS since 1979. This decrease in SOM could reduce nutrient availability and consequently reduce the production capacity of this inherently low SOM soil. The quantities of crop residue that can be sustainably harvested are directly influenced by initial SOM concentration of a soil. Large-scale residue removal for bioenergy must be balanced with other critical functions that agricultural lands provide, including nutrient and water cycling, and C sequestration, for the maintenance of soil productivity. More long-term field data is required to validate predicted SOM stocks under a wide range of soil, climatic conditions, and management practices including crop residue harvest scenarios. [GRACEnet and REAP publication].