Sainju, Upendra (USDA-ARS, 1500 North Central Avenue, Sidney, MT, 59270;

Phone: 406-433-9408; Fax: 406-433-5038; Email: usainju@sidney.ars.usda.gov)

Carbon Sequestration in Dryland Soil and Plant Residue as Influenced by Tillage and Crop Rotation

U. M. Sainju*, A. Lenssen, T. Caesar Ton-That, J. Waddell

Management practices may influence crop biomass yield and C sequestration in plant residue and soil in drylands of northern Great Plains. We examined the effects of two tillage practices [conventional till (CT) and no-till (NT)], five crop rotations [continuous spring wheat (CW), spring wheat-fallow (W-F), spring wheat-lentil (W-L), spring wheat-spring wheat-fallow (W-W-F), and spring wheat-pea-fallow (W-P-F)], and grasses under Conservation Reserve Program (CRP) on plant biomass (stems + leaves) returned to the soil, residue cover, amount, and C content, and soil organic C (SOC) and particulate organic C (POC) contents at 0- to 5- and 5- to 20-cm depths. A split-plot field experiment was conducted in a mixture of Elloam clay loam (fine-loamy, mixed, Aridic Argiborolls) and Kevin clay loam (fine, montmorillonitic, Aridic Argiborolls) from 1998 to 2003 in Havre, MT. Plant biomass yield varied by crop rotation and year and total biomass returned to the soil from 1998 to 2003 was greater in CW (15.3 Mg ha^-1) than in other rotations. Residue cover, amount, and C content in 2003 were 33 to 86% greater in NT than in CT and greater in CRP than in crop rotations. Residue amount (2.47 Mg ha^-1) and C content (963 kg ha^-1) was greater in NT with CW than in other treatments, except in CT with CRP and W-F and in NT with CRP and W-W-F. The SOC at 0- to 5-cm was 23% greater in NT (6.4 Mg ha^-1) than in CT. The POC was not influenced by tillage and crop rotation, but POC/SOC ratio at 0- to 20-cm was greater in NT with W-W-F than in CT with CW, W-F, and W-L. From 1998 to 2003, SOC at 0- to 20-cm was decreased by 4% in CT but was increased by 3% in NT. Carbon can be sequestered in dryland soils and crop residue using reduced tillage and increased cropping intensity, such as NT with CW, compared with traditional practice, such as CT with W-F system, thereby helping to improve soil quality and productivity and reduce soil erosion.