Improved Soil Cover Method for Field Measurement of Nitrous Oxide Fluxes

Abstract

Most researchers agree that soil cover methods offer the most useful approach to measuring nitrous oxide (N 2 O) exchange in the field, but there is little uniformity in the design of covers used by them. The cover design least subject to the potential errors associated with this approach is a vented enclosure with either closed‐loop air circulation or no forced air circulation. Although the soil N 2 O concentration gradient beneath these covers decreases with time as the gas accumulates, this problem can be overcome by a proposed change in the equation for computing flux from the increase in head‐space N 2 O concentration. Over a broad range of sampling conditions, N 2 O fluxes computed from the new equation were independent of the time allowed for N 2 O accumulation. Other equations were developed that predict optimum soil cover vent dimensions for effectively transmitting ambient pressure fluctuations to the enclosed space while minimizing loss of the accumulating N 2 O by diffusion to the outside. Soil covers with vent dimensions dictated by the equations had N 2 O accumulation rates significantly higher than covers with 60% smaller vent diameters but not significantly different than covers with 60% larger vent diameters.