Soil Organic Matter Assessments In A Long-Term Cropping System Study

Assessing effects of cropping systems on soil organic matter (SOM) and soil carbon (C) changes are necessary to make accurate projections regarding sequestration and emission of CO2 by agricultural soils. This process requires substantial annual management inputs and large outlays for soil sampling and analyses. Our objectives were (1) to evaluate and test an alternative method for soil organic matter determination, (2) to determine if crop rotation and N fertilizer management significantly affected soil organic matter at the beginning (1986) or after 12 yrs (1998), and (3) to determine if total soil organic matter levels have changed after 12 years in a long-term cropping system study. Soil samples were taken in 1986 and 1998 to a depth of 150 cm in 30 cm increments. Total soil organic C and organic matter by weight loss-on-ignition concentrations were determined for the soil samples taken in 1998. Results from both methods of analyses for the 1998 samples were highly correlated. No significant differences in soil organic matter by weight loss-on-ignition or total soil organic C concentrations between crop rotations or nitrogen (N) fertilizer rates were obtained for either sampling date, in the change in soil organic matter concentrations between dates, or total soil C amounts in the profile (0 to 150 cm) after 12 yrs (1998). Although no differences in soil organic matter (soil C) were obtained in the study, the excellent correlation between results of the two methods of organic matter analyses demonstrates that the less expensive and easier to use weight loss-on- ignition method can be used to make these types of assessments