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A Computer Simulation Model for Soil Genesis Applications¹

ABSTRACT

A two horizon computer model was developed to simulate leaching and acidification processes occurring in the solid phase of soils of humid, temperate climates. The model used linear equations to describe processes of sulfate adsorption, cation exchange, mineral weathering, and precipitation and dissolution of sesquioxides within the soil. Standard soil characterization and precipitation chemistry data were used as inputs to quantitatively predict changes in soil properties over time. T-test analysis showed no significant difference at the 0.01 level between field values and those predicted by the model for base saturation, pH, and exchangeable cations. Two examples illustrated the application of the simulation model for soil genesis investigations. In the first example, acidic soils with low buffer capacities reached 60% base saturation (Ultic Hapludalfs) and 35% base saturation (Typic Hapludults) sooner than more basic soils. Using regression analysis (excluding soils with high amounts of exchangeable bases), base saturation decreased at a rate of 0.01%/yr under deciduous forest, and 0.02%/yr under coniferous forest at precipitation pH 4.1. At precipitation pH 5.5, the rate of change was much slower. In the second example, a change in soil pH over time was predicted at precipitation pH values of 4.1 and 5.5 under deciduous and coniferous forest vegetation. In all simulations, a "steady state" soil pH level was predicted, with soils under coniferous forest reaching this level sooner than those under deciduous forest. The steady state pH was lower under precipitation pH 4.1 than under pH 5.5.

¹ Authorized for publication as paper no. 7168 of the journal series of the Pennsylvania Agricultural Experiment Station, University Park, PA 16802.

² Former Graduate Assistant and Professor of Soil Genesis and Morphology, Dep. of Agronomy, The Pennsylvania State Univ., University Park, PA 16802.

Received for publication August 29, 1985.