Nitrogen Affects Wheat and Canola Silica Accumulation, Soil Silica Forms, and Crusting

Raindrop-induced crusting of mineral soils supporting wheat ( L.) in the semiarid US Pacific Northwest reduces seedling establishment of late summer-seeded winter crops during dry, hot conditions. Canola ( L.) integration is diversifying regional food, feed and fuel global markets. Subsequent shifts in recycled crop residue characteristics, including Si and crop fiber, may shift soil characteristics of traditional wheat-dominated systems, potentially affecting their propensity to form soil crusts. In a greenhouse study, wheat and canola were fertilized with varying N rates. Increased N supply increased transpiration, shoot weight, and hemicellulose and cellulose yields, but with only minor increases in shoot Si and lignin yields. Both crops had similar increases in root Si with greater N-stimulated transpiration. Two subsequent soil incubations were conducted to determine how Si, N fertilization, and crop residues from wheat and canola affected soil properties. In the first incubation, Si was applied as aqueous HSiO, which increased soil amorphous and water-soluble Si (Si and Si), physical resistance, and crust thickness. Electron micrographs showed increased amorphous material, presumably a Si precipitate, on soil particles with increased Si application. Second, two Ritzville soils were treated with the canola or wheat shoot residues with and without N fertilizer. Nitrogen lowered soil pH, Si, Si, surface resistance, and crust thickness; however, first-time application of crop residue types had no short-term effect on these parameters. Any impacts of lower Si returned by lower Si crop residues on soil physical properties likely require several rotational cycles of Si crop uptake and residue returns.