Monday, November 13, 2006 - 2:30 PM

Cover Crops and Sampling Dates Effect on Soil Carbon Pools under Conservation Tillage Cotton.

Upendra Sainju1, Harry Schomberg2, Bharat Singh3, Wayne Whitehead4, P. Glynn Tillman1, and Sharon Lachnicht Weyers5. (1) USDA-ARS, USDA-ARS-NPARL, 1500 N Central Ave., Sidney, MT 59270, (2) USDA/ARS, 1420 Experiment Station Rd., 1420 Experiment Station Rd., Watkinsville, GA 30677-2373, United States of America, (3) Agric. Research Station, 1005 State University Dr., 1005 State University Dr., Fort Valley, GA 31030-4313, United States of America, (4) Fort Valley State Univ., Fort Valley State University, Po Box 5744 Ag. Res. Station, Fort Valley, GA 31030-4313, (5) USDA-ARS North Central Soil Consv., 803 Iowa Avenure, 803 Iowa Avenure, Morris, MN 56267, United States of America

Cover crops may influence soil C sequestration and microbial activities by providing additional residue C to soil. We examined the influence of legume (crimson clover), nonlegume (rye), blend (a mixture of legumes containing balansa clover, hairy vetch, and crimson clover), and rye + blend mixture cover crops on active and slow pools of soil C at 0-15 cm depth from 2001 to 2003 in irrigated and dryland cotton in Georgia. Total aboveground cover crop and cotton C input was 9 to 32% greater in rye + blend than in other cover crops in 2001 but was 24 to 59% greater in rye than in blend and rye + blend in 2002. In dryland cotton, PCM at the 5-15 cm depth was greater in June 2001 and 2002 than in January 2003 but MBC at 0-5 and 5-15 cm had opposite trend. In irrigated cotton, SOC was greater with rye + blend than with crimson clover. The PCM at 0-5 cm was greater with blend and rye + blend than with rye in April 2001 but was greater with crimson clover than with rye and rye + blend in March 2002. The MBC at 0-5 cm was greater with blend than with rye and crimson clover in April 2001 but was greater with rye, blend, and rye + blend than with crimson clover in March 2002. Soil active C pools varied between summer and winter due to differences in temperature, moisture, and substrate availability in dryland cotton. In irrigated cotton, lower C/N ratio of legume cover crops increased C mineralization in the spring but greater residue C from legume and nonlegume cover crop mixture and succeeding cotton increased soil C storage.