ARS | Publication request: Soil Organic Carbon Changes with Depth: Effects of Tillage and Crop Rotation

Submitted to: International Symposium on Soil Organic Matter Dynamics: Land Use, Management and Global Change
Publication Type: Abstract Only
Publication Acceptance Date: June 17, 2009
Publication Date: July 1, 2009
Citation: Gollany, H.T., Albrecht, S.L., Roager Jr, N.C., Polumsky, R.W. 2009. Soil Organic Carbon Changes with Depth: Effects of Tillage and Crop Rotation. Conference Proceeding of International Symposium on Soil Organic Matter Dynamics: Land Use, Management and Global Change. July 6-9, 200. P.225

Technical Abstract: Decades of wheat-fallow rotation with intensive tillage have resulted in reduced soil organic carbon (SOC) content in the Pacific Northwest dryland region. Adoption of alternative cropping systems such as intensive cropping, direct seeding or sweep tillage (ST) has been slow because of limited available long-term data on the viability of alternative cropping systems in this semiarid region. The objective of this study was to determine effects of tillage and cropping systems on SOC stocks of a Typic Haploxeroll. A randomized complete block design alternative tillage and crop intensity study commenced at Pendleton in 1998 with the following treatments: 1) continuous winter wheat (Triticum aestivum L.) under direct seeding (no-tillage), CW/DS; 2) winter wheat–winter wheat–sudangrass (Sorghum sudanese L.) rotation under direct seeding, W–W–S/DS; and 3) winter wheat–fallow under sweep tillage, W–F/ST. Using a grid scheme, six geo-referenced soil cores per plot were collected in 2004 and 2008. Cores were sectioned at 0-5, 5-10, 10-20, 20-30, 30-60, 60-100, 100-120, and 120-150 cm. Organic and inorganic C were determined at each soil depth. Wheat yield, and residue yield for wheat and sudangrass were measured. Results from the alternative tillage and crop intensity study were compared with an adjacent long-term conventional (inversion moldboard plow, MP) wheat-fallow rotation and control (permanent chemical fallow, CF) treatment. After 10 years of direct seeding and increased crop intensity, very significant (P <0.0001, n = 42) amounts of C were found down to the 150-cm depths. Compared to W–F/MP, SOC increased at the 0-5, 5-10, 10-20, 20-30, 30-60, 60-100, 100-120, and 120-150 cm depths by 16, 5, 1, 6, 25, 33, and 44% under CW/DS, respectively. The SOC in the top 5 cm increased by 14, 16, 32 and 43% for W–F/ST, CW/DS, CF, and W–W–S/DS, respectively, compared to W–F/MP. Increased SOC is expected to reduce losses of soil, water, plant nutrients and agrichemicals. [GRACEnet Publication]