Elevated atmospheric CO2 in agroecosystems:: Soil physical properties

Increased crop biomass production caused by elevated atmospheric CO2 concentration suggests more carbon input to the soil, which could alter soil physical properties. Soil samples were collected from the surface layer (0-6 cm) after 5 years of soybean [Glycine max (L.) Merr.] or sorghum [Sorghum bicolor (L.) Moench.] production under two CO2 levels (360 muLL(-1) and 720 muLL(-1)) on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults) under no-till management using open top field chambers in Auburn, Alabama. Soil carbon content, bulk density, saturated hydraulic conductivity, and water stable aggregates were measured. Soil carbon content was increased by elevated CO2. Significant cropping system by CO2 interactions were noted for soil bulk density and saturated hydraulic conductivity; aggregate stability exhibited a similar trend. In the soybean system, soil bulk density decreased whereas saturated hydraulic conductivity and aggregate stability increased as a result of elevated CO2; however, CO2 had little affect on soil properties in the sorghum system. Results indicate that greater nonyield biomass inputs could increase soil carbon content and improve soil physical properties, especially in soybean production systems.