QUANTIFYING CHANGES IN SOIL PHYSICAL-PROPERTIES FROM SOIL AND CROP MANAGEMENT - A SURVEY OF EXPERTS

A questionnaire was developed to investigate relationships between soi l physical properties and tillage practices. The purpose was to develo p a knowledge base which could quantify these relationships and be tra nslated readily into rules for use in the BESTAQUA hydrologic simulati on model and expert system. Experts were asked to evaluate the effects on soil physical properties of four tillage practices, two soil types , three times of the season, and one or two soil depths in a corn-soyb ean rotation. Soil properties included surface crop residue, surface s torage volume, macropores which were continuous to the surface, soil o rganic matter bulk density, saturated hydraulic conductivity, and plan t available water capacity. Thirty-two respondents (58% response rate) provided soil property estimates. From these data, means and confiden ce interval ranges provided a quantitative approximation of the relati ve expected changes in soil properties with tillage practice, crop yea r of a rotation, time of season, and soil depth and type. The means an d ranges of the relative changes were compared with literature data: a nd interpreted drawing upon the information-rich qualitative feedback from the experts. Confidence interval ranges of these trends were gene rally found to span the ranges of values found in the literature and s howed that management practices significantly influence soil propertie s. These results provide a set of reasonable and comprehensive values for estimating the relative effects of tillage management on soil phys ical properties, and present an opportunity to improve many agricultur al hydrologic models and equations by including the effects of tillage -induced soil physical properties changes summarized in this study.