Metabolic Activity and Soil Quality in Four Midwestern Watersheds.

The Crop land Effects Assessment Project (CEAP) was initiated in the U.S. to provide a scientific basis for assessing the effectiveness of conservation practices on water and soil quality.  In 2006, in sampling was initiated within a number of USDA-ARS experimental watersheds to measure and assess management impacts on near-surface (0-15 cm) soil quality indicators. In this study we focused on four Midwestern watersheds located in Indiana, Iowa, Ohio and Missouri (>700 samples), primarily in corn-based rotations.  In addition to chemical, physical, and nutrient indicators, we quantified soil organic carbon (SOC), microbial biomass carbon, potentially mineralizable carbon and nitrogen, and β-glucosidase (BG), N-acetyl 1,4 glucosaminidase (NAG), arylamidase (AM) acid phosphatase (AP), and fluorescein diacetate (FDA) . All enzymes were influenced by soil order and, with the exception of NAG and FDA, texture. Due to interactions between of soil type, SOC and management systems, system impacts had to be determined on each watershed separately. Use of manure amendments and cover crops increased all enzyme activities except NAG. For tillage management perennials >no-till >rotational ≈ conservation > conventional for BG, AM, AP and FDA. In explaining the variation in specific enzyme activities, other enzyme activity levels were important, as were C_min, Fe, Cu and/or Zn levels. This study highlights the interdependence enzyme activities with each other as well as with other markers of microbial activity and micronutrients. While BG, AM, AP and FDA can be useful for discriminating between management systems, NAG was not.