Tuesday, November 6, 2007
204-1

Changes in Soil Organic Carbon of Crop Rotations in the Northern Corn Belt.

Joseph L. Pikul Jr., USDA ARS North Central Agricultural Research Laboratory, 2923 Medary Ave., Brookings, SD 57006, Thomas E. Schumacher, Plant Science Department, South Dakota State University, NPB 247A, Brookings, SD 57007, Merle Vigil, USDA ARS Central Great Plains Research Station, 40335 County Rd. GG, Akron, CO 80720-1029, and Walter E. Riedell, USDA-ARS North Central Agricultural Research Laboratory, 2923 Medary Ave., Brookings, SD 57006.

Diversified crop rotation may reduce fertilizer nitrogen (N) input for corn (Zea mays L.) and increase soil organic carbon (SOC) storage. Objectives were to determine effect of rotation and N on soil C sequestration. The experiment, started in 1990, was on a Barnes sandy clay loam near Brookings, SD. Since 1996, primary tillage was chisel plow on all rotations. Prior to 1996, moldboard plow was used. All crop residues were returned to the soil. Crop rotations were: continuous corn (CC), corn-soybean [Glycine max (L.) Merr.] (CS), and a four-year rotation of corn-soybean-wheat (Triticum aestivum L.) companion seeded with alfalfa (Medicago sativa L.)-alfalfa hay (CSWA). Non-cropped treatments included warm, cool, and a mix of warm and cool season perennial grasses. Nitrogen treatments for corn were: corn fertilized for a grain yield of 8.5 Mg/ha (N1), 5.3 Mg/ha (N2), and no N (noN). During a four-year cycle, 35 percent less tillage was used on CSWA compared to CC. Corn yield under CSWA with noN was 91% of the yield attained under CC with N1. Soil organic C (0 to 15 cm) under grass increased 3.75 Mg C/ha from 1996 to 2006. Continuous corn under N1 returned about 1.6 times as much above-ground plant C to the soil as CSWA. Under N1, there was a loss of -2.3 Mg C/ha (0 to 15 cm) from CC and a gain of 0.3 Mg C/ha from CSWA (1996 to 2006). A combination of increased crop diversity and less tillage on CSWA, compared with CC, resulted in quasi-equilibrium soil conditions where C return was balanced by C lost. In contrast, corn stover return of 7.02 Mg/ha/year (average 1990 to 2005) under CC with N1 was not enough to balance SOC loss.

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