Applying a soil quality index to conventional, integrated, and organic apple production systems

We used a quantitative index to assess the effects of conventional, integrated, and organic apple production systems on soil quality in the Yakima Valley of Washington state, USA (latitude 46 degrees 30' N). Four replicate plots for each apple management system were planted in a randomized, complete block design on a 1.7 hectare commercial 'Golden Delicious' apple (Malus domestica Burkh.) orchard at a density of 2430 trees per hectare. The site had been in grass pasture prior to planting the apple trees in May, 1994. The study area is made up of Cleman and Shano very fine sandy loams which are coarse-loamy mesic Xerifluventic Haplocambids. The soil quality index we used is a weighted additive model of the soil's capacity to accommodate water entry, facilitate water transfer and absorption, resist degradation, and sustain crop productivity and quality. We determined critical threshold values and relative importance for each soil property based on published data and soil conditions in adjacent permanent grass sites. Soil quality was higher under both the integrated and organic apple production systems, as these systems resulted in increased surface water infiltration, higher microbial biomass carbon and nitrogen, greater surface aggregate stability, and more earthworms than the conventional system. Our goal for developing such site-specific soil quality indices is to assist researchers, consultants, and producers in evaluating long-term effects of specific farm management systems on soil quality.