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.

Keywords:

• Greenhouse gas
• Nitrous oxide flux
• Soybean
• Rainfall
• Mississippi alluvial soil

Acknowledgments

Thanks to Dr. William Patrick for his support. Thanks to the WBI members and staff for the hospitality. Thanks to Roy Iwai for helping in collecting and analyzing some samples. To Keith Whitehead from the Ben Hur LSU Campus from his technical support, and to Dr. Thomas Bride for the meteorological data.