Tuesday, November 14, 2006 - 9:30 AM

Soil Phenol Oxidase Enzyme Activity and Carbon Stabilization in No-tillage Systems.

Soraya Alvarado1, John H. Grove2, Christopher Matocha3, and Elisa D'Angelo3. (1) Univ. of Kentucky, Agronomy Dept S-12 ASCN, Lexington, KY 40546-0091, (2) Univ. of Kentucky, Dept. of Plant and Soil Sciences, N122L Ag Sci Ctr - North, 500 S. Limestone St., Lexington, KY 40546-0091, (3) Univ. of Kentucky, Lexington, KY 40546-0091

Phenol oxidase enzymes play an important role in soil carbon stabilization by favoring the formation of humic substances through catalysis of polyphenol oxidation reactions. Nevertheless, the response of phenol oxidases to soil management practices is not fully understood for no-tillage systems, which are characterized by high organic matter contents, very active microbial populations, and, consequently, high extracellular enzyme activity. Accordingly, this study evaluated phenol oxidase enzyme activity as a sensitive indicator of carbon stabilization as modified by several no-tillage soil management practices. Three long-term field experiments located near Lexington, Kentucky were studied. In the first experiment, two tillage treatments [moldboard plow and no-till] and two nitrogen rates (0 and 150 kg N/ha) were sampled. In the second experiment the five corn components of three continuous no-till crop rotations (monoculture corn, corn-wheat/doublecrop soybean, and forage-forage-corn-corn-corn) were sampled. In the third experiment soil samples were taken from unmanured and manured (spring of each year) main plots at each of two nitrogen rates (0 and 168 kg N/ha). Soils were sampled at the 0 to 10 and 10 to 20 cm depth increment. Physical-chemical characterization included bulk density, texture, aggregate size distribution, pH, total and dissolved organic carbon, total and dissolved organic nitrogen, and inorganic nitrogen as NH4+ and NO3-. Soil biological characterization included soil microbial biomass carbon and nitrogen, and also phenol oxidase activity. Relationships among the studied parameters will be discussed.