Soil-Surface Carbon Dioxide Efflux of Bioenergy Cropping Systems.

Bioenergy cropping systems have been proposed as a way to enhance United States energy security.  However, research on greenhouse gas emissions from such systems is needed to ensure environmental sustainability in the field.  Since soil aeration properties are dynamic, high-resolution data are needed to capture their temporal and spatial variability and relations.  The objective of this study is to quantify soil-surface carbon dioxide emissions among various bioenergy cropping systems and evaluate emission relationships to soil physical conditions.  Cropping systems evaluated include mixed prairie (nitrogen-fertilized and unfertilized), continuous maize with 50 % stover removal (with and without cover crop), and maize-soybean rotation (each crop type grown each year) with four replications in a randomized complete block design.  The site is located on Typic Endoaquoll and Aquic Hapludoll soils near Ames, Iowa.  Soil-surface carbon dioxide efflux was measured at various intra-crop management zones and over time.  Plots were instrumented to continuously measure soil temperature and water profiles whereas select plots were instrumented to continuously measure CO₂ and O₂ concentration and air pressure profiles. Soil-surface carbon dioxide effluxes were significantly greater under prairie systems than row crop systems both early and late in the growing season but had no differences during the mid-summer months.  Soil-surface carbon dioxide efflux varied among intra-crop management zones with time and soil physical conditions which may give knowledge allowing the adaptation of models to more accurately estimate annual or growing season carbon dioxide efflux based on field data.