Soil enzyme activities and physical properties in a watershed managed under agroforestry and row-crop systems

The proportion of water-stable aggregates (WSA) and a diverse microbial activity influence soil quality, crop growth, nutrient retention, water infiltration, and surface runoff. The objective of the study was to test the hypothesis that permanent vegetative buffers increase WSA and contribute to increased soil enzyme activity. Soil samples (5 cm diameter and 10 cm long) from agroforestry (AG), grass buffer (GB), grass waterway (GWW) and crop (CS) areas were collected from summit, middle, and lower landscape positions at the Paired Watershed Study, near Novelty, MO. Water-stable aggregates (>250 μm diameter; wet-sieving method), soil carbon, and soil enzyme activity were determined and data were statistically analyzed. Soils under permanent vegetative buffers and GWW had significantly lower bulk density and more WSA than the crop areas. Soil carbon contents were highest in the GWW and lowest in the CS treatments. Fluorescein diacetate (FDA) hydrolase, β-glucosidase, and glucosaminadase enzyme activities were higher in AG, GB, and GWW soils than CS soils. Dehydrogenase activity differed between grass buffer or GWW and crop areas. The results of the study show that WSA, soil carbon, and functional diversity of enzyme activity increased due to establishment of buffers with trees and grass. It can be speculated that increased diversity of functional enzymes associated with cycling of key soil nutrients and improved soil physical properties may reduce nonpoint source pollution (NPSP) from row-crop agriculture watersheds thus improving overall environmental quality.