Gollany, Hero (USDA-ARS, Pendleton, OR, 48037 Tubbs Ranch Roads, Adams, OR, 97810; Phone: 541-278-4410; Fax: 541-278-4372; Email: hero.gollany@oregonstate.edu)

Incorporated Source Carbon and Nitrogen Fertilizer Influence on Sequestered Carbon and Soluble Silica in a Pacific Northwest Mollisol

H.T. Gollany *, R.R. Allmaras, S.L. Albrecht, S.M. Copeland, C.L. Douglas, Jr.

Long-term experiments are ideal for evaluating the influence of agricultural practices on soil organic carbon (SOC) and its interaction with soil constituents. Limited research has examined influence of organic amendments on SOC and silica (Si) interaction. The objectives were to: i) determine the effect of residue management and organic amendments on SOC accretion; and ii) evaluate the influence of organic amendments on fine organic matter (FOM) distribution and interaction with soluble Si. A long-term fallow-wheat (Triticum aestivum L.) experiment with several residue management practices (NB, no burn; SB, spring burn; and FB, fall burn), three N rates (0, 45, and 90 kg N ha^-1), and organic amendments (NB_M, 11.2 t/ha/yr manure; and no burn pea vines, 1.12 t/ha/yr pea vines) was established on a Walla Walla silt loam (coarse-silty, mixed, superactive, mesic Typic Haploxeroll) in 1931. The experiment is an ordered block with 2 replications. Soil cores (2-cm depth increments) were used to measure coarse organic matter, FOM, pH, bulk density, water-soluble C and water-soluble Si. The SOC storage for the NB_M (5.78 kg C m^-2) was 25% higher than FB₀(4.62 kg C m ^-2) at the 0-50 cm depth. Nitrogen fertilizer application decreased water-soluble Si by 17% while manure or pea vines application increased water-soluble Si by 10%. Silica solubilization and movement in response to reduced pH was greater in the absence of organic amendments. Increased SOC and associated reduction in Si solubilization suggest that biological SOC sequestration impacts siliceous pan formation and enhances drainage.