Comparison of five soil organic matter decomposition models using data from a super(14)C and super(15)N labeling field experiment

Five alternatives of the previously published MOMOS model (MOMOS-2 to -6) are tested to predict the dynamics of carbon (C) and nitrogen (N) in soil during the decomposition of plant necromass. super(14)C and super(15)N labeled wheat straw was incubated over 2 years in fallow soils of the high Andean Paramo of Venezuela. The following data were collected: soil moisture, total super(14)C and super(15)N and microbial biomass (MB)- super(14)C and - super(15)N, daily rainfall, air temperature and total radiation. Daily soil moisture was predicted using the SAHEL model. MOMOS- 2 to -4 (type 1 models) use kinetic constants and flow partitioning parameters. MOMOS-2 can be simplified to MOMOS-3 and further to MOMOS-4, with no significant changes in the prediction accuracy and robustness for total- super(14)C and - super(15)N as well as for MB- super(14)C and - super(15)N. MOMOS-5 (type 2 models) uses only kinetic constants: three MB- inputs (from labile and stable plant material and from humified compounds) and two MB-outputs (mortality and respiration constants). MOMOS-5 did not significantly change the total- super(14)C and - super(15)N predictions but markedly improved the predictive quality and robustness of MB- super(14)C and - super(15)N predictions (with a dynamic different from the predictions by other models). Thus MOMOS-5 is proposed as an accurate and ecologically consistent description of decomposition processes. MOMOS-6 extends MOMOS-5 by including a stable humus compartment for long-term simulations of soil native C and N. The improvement of the predictions is not significant for this 2-year experiment, but MOMOS-6 enables prediction of a sequestration in the stable humus compartment of 2% of the initially added super(14)C and 5.4% of the added super(15)N.