Monday, November 13, 2006

Comparison of Soil Physical Properties under Organic and Conventional Management Systems.

Jeffrey S. Strock1, Stacey Burns1, Deborah Allan2, Jennifer King1, and Jay Bell1. (1) Univ of Minnesota, 23669 130th St, Lamberton, MN 56152-1036, (2) 1991 Upper Buford Circle, University of Minnesota, University of Minnesota, Soil, Water, Climate Department, St. Paul, MN 55108

Soil physical properties are important soil quality indicators, as they have important agricultural and environmental implications and are strongly affected by land management practices. The objective of this study was to measure the effects of organic and conventional management practices on soil physical properties including: bulk density, infiltrability, sorptivity, soil water retention, and vertical saturated hydraulic conductivity (Ks). Soil samples were collected during 2004 from the Elwell Agroecology Farm (EAF) at the University of Minnesota Southwest Research and Outreach Center located near Lamberton, Minnesota. Soil types were a complex of Ves, Normania, and Webster, clay loams (fine-loamy, mixed mesic Calcic Hapludolls; fine-loamy, mixed, mesic Aquic Hapludolls; and fine-loamy, mixed, mesic Typic Endoquolls, respectively). These three soil types represented well, moderately, and poorly drained soils on the upper, mid, and bottomslope landscape positions in this gently rolling glacial till landscape. Bulk density in the A horizon was lower under organic management practices than under conventional practices. Infiltrabiltiy and saturated hydraulic conductivity were significantly higher in the A horizon under organic management practices than under conventional management. Differences in conductivity were greater for soils located at bottomslope positions than soils at mid- or upper-slope positions. The b value of Campbell's moisture retention equation was significantly smaller for organic practices than conventional management practices in the A, B, and C horizons. The Campbell equation air entry value was significantly larger for organic practices than conventional practices in the A horizon. Differences in bulk density, air entry, and Ks between the organic and conventional management systems were attributed to differences in crop rotations and tillage management between the two systems. These differences in physical and hydraulic properties can be used by modelers to estimate the impacts of alternative versus conventional agricultural practices on water movement and water quality.