Modeling the genesis of luvisols as a function of topographic position in loess parent material

A simulation model SoilGen2 was developed to simulate aspects of soil formation under a range of climatic conditions (udic, ustic, xeric and aridic moisture regimes and cryic, frigid, mesic and thermic soil temperature regimes), various parent materials, vegetation types, slopes and expositions. Simulated processes include water, solute and heat flow, C-cycle, bioturbation, physical weathering and clay migration. After a calibration of the calcite dissolution constant and parameters affecting clay migration, modeling results after 15,000 years were confronted with today’s measurements at 3 positions in a toposequence in loess. The model was able to simulate the formation of A, E and Bt-horizons and decalcification of the loess, and responded to local differences in exposition and slope in a way confirmed by measurements along the toposequence. Best values for dissimilarity were obtained for organic carbon, sand % and CEC. Results indicate that simulation quality is sensitive to adequate estimation of precipitation, potential evapotranspiration and evaporation from leaf interception. Likewise, an accurate reconstruction of the initial condition of the parent material in terms of calcite content, bulk density and clay content is important to allow correct estimates of clay transport and decalcification.