Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 9, 2000
Publication Date: N/A
Using the dry combustion (DC) method for measuring soil carbon requires extensive soil grinding, mixing, and accurate weighing to prepare a 10 to 15 mg subsample from an original soil sample of 50 g or larger. As a result, this method is sensitive to inclusion or exclusion of individual particles of soil organic matter or plant residues in the micro-sample that is analyzed, which may skew the result. Additionally, the labor and expense of processing samples often limits the number of samples taken, which makes characterization of treatment differences or spatial variability difficult. The weight-loss-on-ignition (WLOI) method is much simpler, requires less labor, and allows the carbon content of an entire sample to be measured without grinding, mixing, or subsampling. The procedure we use requires taking accurate weights of soil cores before and after heating to 360 C for 16 h. The linear regression of WLOI measurements on DC measurements had an R2 = 0.92. In general, the coefficients of variation for the WLOI method were smaller than those for the DC method. We used the WLOI to show that the spatial variability of soil carbon in an agricultural field is very large and that this large variation makes it extremely difficult to detect changes in soil carbon caused by cover crops in a corn-soybean rotation.