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Comparison of Field Denitrification Rates Determined by Acetylene-Based Soil Core and Nitrogen-15 Methods¹

ABSTRACT

A soil core method to measure field denitrification rates was evaluated by comparing the results with denitrification rates measured by the ¹⁵N difference method. In the core method, acetylene amended air was recirculated through an undisturbed soil core and short-term (ca. 1 h) nitrous oxide production monitored. Denitrification rates were obtained on soil cores from two field sites and a set of sieved, repacked soil cores in a laboratory incubation. Cumulative N-losses were estimated by interpolating between sample dates. Denitrification rates obtained by the core method were found to approximate a log normal distribution at both sites studied and at all sampling times. Statistical calculations appropriate for this distribution resulted in improved estimates of the mean rates and confidence intervals. For the ¹⁵N difference method, ¹⁵N enriched nitrate was added to microplots of 30 cm diameter and the total gaseous losses were estimated by considering the change in the total nitrate pool, the isotope ratio of that pool and the ¹⁵N not recovered from the microplots. Experiments were conducted over periods of 32 to 45 d on sandy loam and clay loam soils, respectively. Denitrification rates from the acetylene-core method were not significantly different than the estimates by the ¹⁵N method. Denitrification rates as measured by both methods were highly variable.

¹ Contribution from the Dep. of Crop & Soil Sciences and of Microbiology & Public Health, Michigan State Univer., East Lansing, MI 48824-1114. Published as Journal Article no. 11211 of the Michigan Agric. Exp. Stn. This work was supported by National Science Foundation Grant DEB-80-12168, USDA Cooperative Agreement no. 58-32U4-1-329 and USDA Regional Research Project NE-39.

² Former Research Associate, Graduate Student and Professor of Soil Microbiology, respectively. Present addresses: T.B.P., Soil Nitrogen & Environmental Chemistry Lab., Beltsville Agric. Res. Center, Beltsville, MD 20705 and A.J.S., Div. of Plant & Soil Sciences, West Virginia Univ., Morgantown, WV 26506.

Received for publication November 4, 1983. Accepted for publication August 6, 1984.