Systematic method for rating soil quality of conventional, organic, and integrated apple orchards in Washington State

Much remains to be known concerning the complex relationships between specific soil property measurements and overall soil quality. The objective of this study was to advance our understanding of these complex relationships by further developing and applying a systematic method for evaluating the effects of conventional, integrated and organic apple production systems on soil physical, chemical, and biological properties using a modified soil quality index. This index utilizes 1998 soils data from these three treatments. The study used four, 0.14 ha replicates of each of the three treatments in a randomized complete block design. Experimental plots were planted to 'Golden Delicious' apples (Malus domestica Borkh.) in 1994 on a commercial orchard in the Yakima Valley of Washington state. Organic soil management practices included additions of composted poultry manure and bark mulches and the use of mechanical tillage for weed control. Conventional soil management practices included additions of synthetic fertilizers and the use of herbicides for weed control. The integrated system utilized practices from each of the other two systems. Increased aggregate stability, microbial biomass, and earthworm abundance were associated with improved soil quality under integrated management when compared to conventional management in 1998. Organic management resulted in lower soil bulk densities and generally improved biological soil properties compared to conventional management. Few significant differences in soil properties were measured between the integrated and organic systems. The integrated production system received a soil quality index rating of 0.92 (out of 1.00), which was significantly higher than the index rating of 0.78 for the conventional production system; the organic production system received a rating of 0.88, which was not significantly different from the other two systems. The study indicates that a well-developed soil quality index can provide an effective framework for evaluating the overall effects of different orchard production practices on soil quality. (C) 2000 Elsevier Science B.V. All rights reserved.