Nitrous Oxide Flux from Soybeans Grown on Mississippi Alluvial Soil

Abstract

Several million hectares (ha) of soybeans are grown in alluvial soils of the Lower Mississippi River Valley. Using a diffusion chamber, nitrous oxide (N2O) flux to the atmosphere was measured over a growing season at a site in Louisiana. The average N2O flux over the soybean season was 2.2 ± 4.0 ng N2O-N cm−2h−1 (over plants) and 2.1 ± 4.5 ng N2O-N cm−2 h−1 over the bare soil. Flux was governed by rainfall events. Maximum fluxes of 11.5 ± 2.1 ng N2O-N cm−2h−1, over plants, and 15.1 ± 5.5 ng N2O-N cm−2 h−1 over soil were measured following 15 inches (381 mm) of rainfall the week prior to flux measurements. The highest mean flux (182 ± 222 ng N2O-N cm−2h−1) was measured following harvest (stubble had been disked into soil) and a 4-inch (102 mm) rainfall event occurred just prior to flux measurements. Emission data showed that rainfall is important in predicting N2O flux from Mississippi alluvial soil used for soybean production. In order to properly quantify N2O flux, it is important to measure flux frequently over a series of rainfall events. Periodic flux measurements without factoring in rainfall may underestimate N2O flux to the atmosphere.