ABSTRACT
The CENTURY model for soil organic matter (Metherell et al., 1993) provides an important framework for predicting changes in soil organic C within agricultural ecosystems and provides a set of parameters used in assessing the influence of production management on soil C storage. For example, the model includes the lignin content of plant residue as an important soil parameter for predicting C sequestration within ecosystems, but limited information is known about fate and transformation of plant residue constituents such as lignin with the formation of stable soil organic matter in agricultural ecosystems. Assessing the status and fate of residue lignin can provide important information about the tendency of the ecosystem to store organic C. Classical chemical methods for assessing composition of soil organic matter are cumbersome and largely arbitrary in their type of characterization. For example, it is difficult to directly relate the classical measurements of humic and fulvic acid to ability of soil to sequester C. New techniques are needed to provide more relevant assessments of compositional changes in soil organic matter in different ecosystems. Analytical pyrolysis has been shown to be a powerful tool for assessing composition of complex organic materials such as forages and wood including information on lignin content (Caballero et al., 1997; Reeves,
Table 1. Statistics on organic C content of soil samples collected from plots under plow and no-tillage management______________________________________________________________________ Source Mean Range Std All samples (n = 179) 13.3 6.13-33.9 4.6
No tillage (n = 90) 14.9 6.13-33.9 5.9
1990; Rodrigues et al., 1999). With the ability to detect lignin, pyrolysis may provide the means to measure important changes in soil organic matter quality such as lignin composition and transforma tion during formation of stable soil C. Evaluation of such parameters will likely be relevant in assessments of the potential for different soil ecosystems to sequester C.
