|Tillman, Patricia - Glynn|
Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2007
Publication Date: 10/5/2007
Citation: Sainju, U.M., Schomberg, H.H., Singh, B.P., Whitehead, W.F., Tillman, P.G., Lachnicht Weyers, S.L. 2007. Cover crop effect on soil carbon fractions under conservation tillage cotton. Soil and Tillage Research. 96(2):205–218. Interpretive Summary: Cover crops have the potential to increase carbon sequestration, organic matter, soil aggregation, water infiltration capacity, water holding capacity and root growth of summer crops and reduced soil erosion and nitrogen leaching compared with no cover crop. Winter cover cropping, followed by conservation tillage, can maintain or increase organic matter level in the degraded soils of southeast USA. An experiment containing legume (crimson clover), nonlegumes (rye), blend (a mixture of legumes containing balansa clover, hairy vetch, and crimson clover], and rye + blend mixture cover crops under conservation tillage cotton was established in the producers’ field from 2001 to 2003 in central and south Georgia. Soil samples were collected from November 2000 to January 2003 to analyze soil carbon pools, such as soil organic carbon (SOC), potential carbon mineralization (PCM), and microbial biomass carbon (MBC). The total amount of carbon returned to the soil from cover crop and cotton residues were greater with rye + blend than with other cover crops. As a result, SOC and MBC were also higher with this treatment than with others. In contrast, PCM was higher with crimson clover and blend than with other cover crops in the spring and summer. Both SOC and PCM decreased from spring to winter. Greater amount of residue or carbon input increased soil carbon storage and microbial biomass but lower carbon/nitrogen ratio of cover crops increased carbon mineralization. Decreased soil temperature and/or nutrient availability probably reduced microbial biomass and activities in the winter than in the spring.
Technical Abstract: Cover crops may influence soil carbon (C) sequestration and microbial activities by providing additional residue C to soil. We examined the influence of legume [crimson clover (Trifolium incarnatum L.)], nonlegume [rye (Secaele cereale L.)], blend [a mixture of legumes containing balansa clover (Trifolium michelianum Savi), hairy vetch (Vicia villosa Roth), and crimson clover], and rye + blend mixture cover crops on active and slow pools of soil C at 0 to 5 and 5 to 15 cm depths from 2001 to 2003. Active pools of soil C included potential C mineralization (PCM) and microbial biomass C (MBC) and slow pool as soil organic C (SOC). On-farm experiments were conducted in Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults) and Tifton loamy sand (fine-loamy, siliceous, thermic, Plinthic Kandiudults) under dryland and irrigated conservation tillage cotton (Gossypium hirsutum L.) in Bartow and Tifton, central and southern Georgia, respectively, in USA. Total aboveground cover crop and cotton C returned to the soil 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 Bartow, PCM at the 5 to 15 cm depth was greater in June 2001 and 2002 than in January 2003 but MBC at 0 to 5 and 5 to 15 cm depths had opposite trend. In Tifton, SOC was greater with rye + blend than with crimson clover. The PCM at 0 to 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 to 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.