Designing a Soil Quality Assessment Tool for Sustainable Agroecosystem Management

Sustainable agroecosystem management generally entails increased management ability and input. Decision making for sustainable management could be enhanced by tools that provide integration and synthesis of soil test results, management priorities, and environmental concerns. Science-based soil quality indices (SQIs) may provide an ecologically based approach needed for land managers to make sustainable decisions. We developed a general approach for choosing the most representative indicators from large existing data sets, combining indicators into location-specific indices of soil quality, and using this index to assess agricultural management practices. We used a poultry-litter management case study to illustrate the design and use of this SQI. Site-specific indices were created using the SQI design framework for two sites with different soil types but similar climatic regimes. At each site we compared alternative poultry-litter management practices: land application of fresh vs. composted poultry litter. The data sets were composed of >40 assays including total organic C, macro- and micronutrients, heavy metals, plant available water, water-stable aggregate, bulk density, and microbial biomass and activity. Multivariate statistical techniques were used to determine the smallest set of chemical, physical, and biological indicators that account for at least 85% of the variability in the total data set at each site. We defined this set as the minimum data set (MDS) for evaluating soil quality. We evaluated the efficacy of the chosen MDS to assess sustainable management by performing multiple regressions of each MDS against numerical estimates of environmental and agricultural management sustainability goals (i.e., net revenues, P runoff potential, metal contamination, and amount of litter disposed of). Coefficients of determination for these regressions ranged from 0.35 to 0.91, with an average R2 = 0.71. We then transformed and combined each MDS into an additive SQI. Index values exhibited significant differences between management treatments. SQI values for composted litter applied at a low rate were consistently highly ranked, but the relative ranking of treatments changed slightly due to differences in inherent soil properties at the two sites. Using this generalized framework allowed indices to be tailored to local conditions. The resulting soil quality index appears to be an effective monitor of sustainable management.