Variation in Soil Enzyme Activities in a Temperate Agroforestry Watershed.

Integration of agroforestry and grass buffers into row crop watersheds has been shown to improve overall environmental quality, including soil quality.  The objective of this study was to examine management and landscape effects on soil carbon, soil nitrogen, microbial diversity, enzyme activity, and DNA concentrations.  Management treatments were row crop (RC), grass buffer (GB), agroforestry buffer (AB), and grass waterways (GWW); and landscape treatments were summit, middle, and lower positions.  The no-till management corn (Zea mays L.)-soybean (Glycine max L.) rotation watershed in northeast Missouri was established in 1991 with buffers implemented in 1997.  Grass buffers, 4.5 m wide and 36.5 m apart, consist of redtop (Agrostis gigantea Roth), brome (Bromus spp.), and birdsfoot trefoil (Lotus corniculatus L.) on contour grass and agroforestry watersheds.  Agroforestry buffers have pin oak (Quercus palustris Muenchh.) trees distributed down the center of the grass buffers.  Soils were collected from two transects extending from the summit to lower landscape positions in June 2007.  Soil enzymes studied include: fluorescein diacetate hydrolase, β-glucosidase, glucosaminadase, dehydrogenase, and phosphatase.  Soil DNA content was determined as an alternative of microbial biomass.  Soil carbon and nitrogen concentrations were significantly different among treatments and landscape positions.  Soil enzyme activities were significantly lower in the row crop treatment as compared to perennial vegetative buffers and grass waterways.  The results of the study show that establishment of AG, GB, and GWW increased soil quality; soil carbon, soil nitrogen, microbial diversity, and enzyme activity