Saturday, 15 July 2006

Sequestration and Vertical Distribution of Organic Carbon and Total Nitrogen under Warm-Season Grasses Relative to Croplands.

Rex A. Omonode1, E.J. Kladivko2, William W. McFee2, and T. J. Vyn2. (1) Purdue Univ, Dept of Agronomy, 994 Edgerton Street, West Lafayette, IN 47906, (2) Purdue Univ, Dept of Agronomy, Lilly Hall of Life Sciences, 915 W State St, West Lafayette, IN 47907-2054

Establishment of grasslands can be an effective means of sequestering soil organic carbon (C) and reducing the atmospheric CO2 that is believed to contribute to global warming. This study evaluated the vertical distribution and overall sequestration of organic C and total nitrogen (N) in soils under Warm-Season Native Grasses (WSNGs) planted 6 to 8 years earlier relative to a corn-soybean crop sequence, and switchgrass relative to tall mixed grasses (big bluestem, indiangrass, and little bluestem). Paired soil samples from 0-15, 15-30, 30-60 and 60-100cm depth increments were taken from WSNGs and adjoining croplands at 10 locations, and from switchgrass and adjoining tall mixed grasses at 4 locations, in Montgomery County, Indiana. Surface soil (0-15cm) organic C concentrations were generally higher in WSNGs than croplands (average: 2.34 and 1.46% C, respectively) but total N concentrations were not different between these land-use systems (average = 0.16% N). Surface soil organic C and N concentrations were also relatively higher for switchgrass (2.25% C, 0.17% N) than tall mixed grasses (2.14 % C, and 0.16% N). In general, significant differences in soil C and N concentrations between WSNGs and croplands were limited to the surface 30 cm and were location-specific, but switchgrass and tall mixed were not significantly different at any depth intervals or locations. Average organic C mass calculated to a 1.0 m depth was 11 % higher in WSNGs than cropland, and 8 % higher in switchgrass than tall mixed grass. However, cumulative soil N was only 1% higher with WSNGs than the corn-soybean rotation. The respective vertical distribution under WSNGs of organic C was 26, 23, 28, and 22%, and of total N mass was 32, 26, 28 and 14%, in the 0-15, 15-30, 30-60, and 60-100 cm depth intervals. The effective annual rate of C sequestration (or C loss retardation) by WSNGs relative to that in the corn-soybean sequence was estimated at 2.9 Mg C ha-1 yr1. These WSNGs may have been even more effective in sequestering organic C had these areas had similar soil nutrient concentrations as their corresponding field crop areas.

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