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TECHNICAL REPORTS

Plant and Environment Interactions

Tillage, Cropping Systems, and Nitrogen Fertilizer Source Effects on Soil Carbon Sequestration and Fractions

^a USDA-ARS, Northern Plains Agricultural Research Lab., 1500 N. Central Avenue, Sidney, MT 59270
^b Dep. of Plant and Soil Sciences, Alabama A & M Univ., P.O. Box 1208, Normal, AL 35762

^* Corresponding author (upendra.sainju{at}ars.usda.gov).

Received for publication May 14, 2007. Quantification of soil carbon (C) cycling as influenced by management practices is needed for C sequestration and soil quality improvement. We evaluated the 10-yr effects of tillage, cropping system, and N source on crop residue and soil C fractions at 0- to 20-cm depth in Decatur silt loam (clayey, kaolinitic, thermic, Typic Paleudults) in northern Alabama, USA. Treatments were incomplete factorial combinations of three tillage practices (no-till [NT], mulch till [MT], and conventional till [CT]), two cropping systems (cotton [Gossypium hirsutum L.]-cotton-corn [Zea mays L.] and rye [Secale cereale L.]/cotton-rye/cotton-corn), and two N fertilization sources and rates (0 and 100 kg N ha^–1 from NH₄NO₃ and 100 and 200 kg N ha^–1 from poultry litter). Carbon fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Crop residue varied among treatments and years and total residue from 1997 to 2005 was greater in rye/cotton-rye/cotton-corn than in cotton-cotton-corn and greater with NH₄NO₃ than with poultry litter at 100 kg N ha^–1. The SOC content at 0 to 20 cm after 10 yr was greater with poultry litter than with NH₄NO₃ in NT and CT, resulting in a C sequestration rate of 510 kg C ha^–1 yr^–1 with poultry litter compared with –120 to 147 kg C ha^–1 yr^–1 with NH₄NO₃. Poultry litter also increased PCM and MBC compared with NH₄NO₃. Cropping increased SOC, POC, and PCM compared with fallow in NT. Long-term poultry litter application or continuous cropping increased soil C storage and microbial biomass and activity compared with inorganic N fertilization or fallow, indicating that these management practices can sequester C, offset atmospheric CO₂ levels, and improve soil and environmental quality.

Abbreviations: CT, conventional till • MBC, microbial biomass C • MT, mulch till • NT, no-till • PCM, potential C mineralization • POC, particulate organic C • SOC, soil organic C