Long-term field experiments with repeated additions of incorporated carbon sources are ideal to examine soil organic carbon (SOC) storage and its interaction with soil constituents. The objectives were to (i) determine the effect of crop residue management, N fertilizer, and organic amendments on SOC storage and (ii) evaluate the influence of source C on fine organic matter interaction with soluble silica (Si). A long-term wheat (Triticum aestivum L.)-fallow experiment with several crop 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 (NBM, 22.4 t ha−1 manure; and NBPV, 2.24 t ha−1 pea vines) was established in 1931 on a Walla Walla silt loam (coarse-silty, mixed, superactive, mesic Typic Haploxeroll). Soil cores (2-cm depth increments) to 50-cm depth were analyzed for coarse organic matter, fine organic matter, pH, bulk density (ρb), water-soluble C (Cws), and water-soluble Si (Siws). The SOC storage for the NBM (5.78 kg C m−2) was 25% higher than that for the FB0 (4.62 kg C m−2) in the 0- to 50-cm depth. Nitrogen fertilizer application (45 or 90 kg N ha−1) decreased Siws by 17%, whereas applied manure or pea vines increased Siws by 10%. Silica solubilization and movement in response to reduced pH was greater in the absence of organic amendments or reduced crop residue returns. Increased SOC storage derived from amendments or N fertilization with a retention of crop residues prevented siliceous pan formation and associated impaired infiltration and internal drainage. Phytolith processes may enhance soil C sequestration and influence the chemistry of both Si and SOC.
1USDA-ARS, Columbia Plateau Conservation Research Center, P.O. Box 370, Pendleton, OR 97801. Dr. Gollany is corresponding author. E-mail: email@example.com
2USDA-ARS, Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55108.
Received Dec. 9, 2005; accepted Mar. 22, 2006.