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 enh anced by tools that provide integration and synthesis of soil test results, management priorities, and environmental concerns. Science-based soil qual ity indices (SQIs) may provide an ecologically based approach needed for la nd managers to make sustainable decisions. We developed a general approach for choosing the most representative indicators from large existing data se ts. combining indicators into location-specific indices of soil quality, an d using this index to assess agricultural management practices. We used a p oultry-litter management case study to illustrate the design and use of thi s SQI. Site-specific indices were created using the SQI design framework fo r two sites with different soil types but similar climatic regimes. At each site we compared alternative poultry-litter management practices: land app lication 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 m icrobial biomass and activity. Multivariate statistical techniques were use d to determine the smallest set of chemical, physical, and biological indic ators that account for at least 85% of the variability in the total data se t at each site. We defined this set as the minimum data set (MDS) for evalu ating soil quality. We evaluated the efficacy of the chosen MDS to assess s ustainable management by performing multiple regressions of each MDS agains t numerical estimates of environmental and agricultural management sustaina bility 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 R-2 = 0.71. We then t ransformed and combined each MDS into an additive SQI. Index values exhibit ed significant differences between management treatments. SQI values for co mposted litter applied at a low rate were consistently highly ranked, but t he relative ranking of treatments changed slightly due to differences in in herent soil properties at the two sites. Using this generalized framework a llowed indices to be tailored to local conditions. The resulting soil quali ty index appears to be an effective monitor of sustainable management.