Long-term experiments are ideal for evaluating the influence of agricultural practices on soil organic carbon (SOC) accretion. Little is known about the influence of tillage and nitrogen (N) fertilization on SOC distribution and silica (Si) movement in a soil. This study: i) determined the effect of tillage and N fertilizer on SOC accretion in a Walla Walla silt loam soil (coarse-silty, mixed, superactive, mesic Typic Haploxeroll), and ii) examined the subsequent influence of fine organic matter on silica movement. A long-term fallow-wheat (Triticum aestivum L.) experiment with two tillages (moldboard plow and sweep) and two N rates (45 and 180 kg N/ha) was established in 1940, in a randomized block with split-plot design and three replications. Soil cores (2-cm depth increments) were used to measure coarse organic matter, fine organic matter, pH, bulk density, water-soluble C, and water-soluble Si. The fine organic matter fraction for the sweep (6.6 kg C/m²) was 14% higher than the moldboard plow (5.8 kg C/m²) for the 180 kg N/ha in the 0- to 60-cm depth. After 44-yr of N addition, the SOC storage for 180 kg N/ ha rate (6.2 kg C/m²) had increased only 3% compared to 45 kg N/ha rate (6.0 kg C/m²). Total water-soluble Si in the B horizon were 34% and 39% greater than in the Ap horizon for the moldboard plow and sweep systems, respectively. Interaction of tillage and N with water-soluble Si suggests that SOC provides a mechanism to suppress Si solubility, which impacts siliceous pan formation, reduces soil mechanical resistance, and enhances drainage and plant growth.