Comparison of five soil organic matter decomposition models using data from a 14C and 15N 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. 14C and 15N 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 14C and 15N and microbial biomass (MB)‐14C and ‐15N, 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‐14C and ‐15N as well as for MB‐14C and ‐15N. 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‐14C and ‐15N predictions but markedly improved the predictive quality and robustness of MB‐14C and ‐15N 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 14C and 5.4% of the added 15N.