Evaluation of Apex to Simulate Management Effects on Soil Properties.

There is a need to provide enhanced information about soil change in response to land use, management or climate change. Changes in dynamic soil properties (DSPs) have been traditionally measured over time through long-term studies and monitoring. Potential changes in DSPs can be estimated using space-for-time substitution comparing land use or management conditions (i.e. vegetation, tillage, climate) on the same soil. To provide comprehensive information about a range of soil and management conditions, field studies must be supplemented using predictive models. The objective of this study was to evaluate the utility of the APEX (Agricultural Policy Environmental eXtender) model to simulate temporal trends in DSPs and the direction of soil change under differing management scenarios. DSP field studies were conducted following the procedures of the USDA Natural Resource Conservation Service Soil Change Guide and were designed to capture changes in soil properties due to management through a space-for-time sampling strategy using locations having the same soil type, for purposes of scaling, but have different conditions (land use and management). The field-scale application of APEX for DSP studies simulates one soil type under multiple land use and management scenarios with one scenario representing the reference state (least disturbed) and one or more representing alternative states (disturbed). Initial results suggest that APEX can adequately predict changes in soil properties and can provide complimentary data to field studies. The population of DSPs from model simulations can be used in conservation tools to assist land managers in their evaluations of likely management impacts on soil properties. Of particular interest is the rate of change and resilience of soils disturbed by cultivation.