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Title: Comparison of methods to evaluate soil and crop management-induced soil carbon changes

Author
item Mikha, Maysoon
item Benjamin, Joseph
item Halvorson, Ardell
item Nielsen, David

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/6/2012
Publication Date: 3/6/2012
Citation: Mikha, M.M., Benjamin, J.G., Halvorson, A.D., Nielsen, D.C. 2012. Comparison of methods to evaluate soil and crop management-induced soil carbon changes. 2012 Great Plains Soil Fertility Conference Proceedings. 14:258-264. March 6-7, 2012. Denver, Colo.

Interpretive Summary: Previous research evaluated soil organic carbon (SOC) mass using SOC concentration and soil bulk density ('b) associated with a specific measured soil depth (fixed-depth). This type of measurement does not consider soil thickness or soil mass that could be influenced by tillage practices. The equivalent soil mass (ESM) calculation method considers the soil thickness and soil mass in evaluating SOC. We compared between the changes in SOC calculated on an equivalent soil mass (ESM) of the 2001 original condition with the SOC calculated on a fixed-depth basis. In addition, we evaluated the application of these calculation methods on the recommended residue-C amount necessary to sustain SOC levels. The experimental design is a split-plot with no-tillage (NT) and chisel plow (CP); the cropping rotations were multiple crops and continuous corn; and the irrigation system was (full and delayed). In 2001 a study was initiated on Weld silt loam soil. At 0-30 cm (12 inches) depth, the ESM over estimated the SOC content by 87% compared with the fixed-depth calculation approach. Consequently, the ESM calculation approach underestimated the amount of crop residue-C required to sustain SOC levels. Apparently, the amount of crop residue carbon required to sustain SOC levels depended on the calculation approaches. Over all, care needs to be taken in assessing SOC using different approaches due to their influences on SOC levels to sustain soil quality and productivity and prevent soil degradation.

Technical Abstract: The majority of previous research evaluated soil organic carbon (SOC) mass using SOC concentration and soil bulk density ('b) associated with a fixed-depth (FD) without considering the soil thickness or soil mass. The objectives of this study are (i) to compare between the changes in SOC calculated on an equivalent soil mass (ESMorg) of the original condition with the SOC calculated on a FD basis; (ii) to compare the application of this calculation methods on the recommended residue-C amount necessary to sustain SOC levels. The experimental design is a split-plot with no-tillage (NT) and chisel plow (CP); the cropping rotations were multiple crops and continuous corn; and the irrigation system was (full and delayed). In 2001 a study was initiated on Weld silt loam soil. After seven years, the SOC at 0-30 cm calculated on ESMorg gained on an average of 6.2 Mg C ha-1 compared with 2001. This approach suggests that the SOC levels could be sustained even by removing the entire crop residue. Apparently, the amount of crop residue-C required to sustain SOC levels depended on the calculation approaches. Calculation approach needs to be carefully addressed due to its influence on SOC levels and residue removal/retention.