Soil Aggregate and Organic Carbon Modeling.

A new soil organic matter (SOM) model is proposed in which the SOM pools are based on measurable fractions. The model integrates an aggregate dynamics submodel with a SOM dynamics submodel. The aggregate submodel simulates the formation and breakdown of macroaggregates and microaggregates. The formation of macroaggregates is assumed to be proportional to microbial activity. The formation of microaggregates occurs preferentially within the stable environment of the macroaggregates. Therefore, this model can simulate the effect of macroaggregate turnover on C storage. Macro- and microaggregate dynamics were calibrated using direct measurements and indirect fitting of literature data from laboratory incubations. Similarly, organic matter dynamics were calibrated using data from SOM fractionation studies of laboratory incubations. The best estimate of macroaggregate turnover rate was linearly related with straw addition. Microaggregate turnover rate was much slower than that of macroaggregates. Nonlinear optimization (minimization) also suggested a significant linear relation between available plant residue and macroaggregate formation rate. A Monte Carlo based sensitivity analysis revealed that SOC was significantly related to the turnover rates of macroaggregates, microaggregates, particulate organic matter, and mineral associated C. The here-presented version is for use in medium-term (<2 year) laboratory incubations. This study presents a proof-of-concept of the novel model, and does not contain an independent validation of all the parameters and coefficients used. Further model development will extend the model for use in long-term field studies.