A Comparison of Oilseed and Grass Crop Residue Silicon and Fiber Composition and Impacts On Soil Quality.

Structural components (e.g. lignin and silicon (Si)) vary between crop types. Grasses, such as wheat, tend to have higher levels of Si and lower amounts of lignin as compared to oilseeds. When such residues are left on the soil surface after harvest, soil crusting can result due to a combination of raindrop impact and the release of Si during the decomposition of high Si containing crops. The two goals of this research are (1) to characterize the specific structural components in wheat and canola residue in order to understand their potential to resist degradation and (2) to grasp the effects of a long-term rotation history on soil crusting.  Wheat (Triticum aestivum L.) and canola (Brassica napus L.) residues grown under different nitrogen (N) rates from a greenhouse experiment were analyzed for neutral detergent fiber (NDF; primarily hemicellulose, cellulose, and lignin), acid detergent fiber (ADF; primarily cellulose and lignin), acid detergent lignin (ADL; primarily lignin), total carbon (C), nitrogen and Si. Wheat residue had proportionately more hemicellulose than canola, at each N fertilizer rate.  In comparison, canola residue was comprised of more cellulose and lignin. Due to its greater biomass production with increasing N, canola accumulated higher amounts of lignin, cellulose, and soluble compounds than wheat. Wheat accumulated 10-times more silica in its residue than canola, and unlike canola, exhibited a decline in %Si at increasing fertilizer levels and thus was diluted at higher yields. In a laboratory incubation, soil was collected from fields previously cropped in winter wheat or winter canola in order to compare the effect of contrasting crop histories on soil crusting. Initial values of soil Si were significantly higher in the soil collected from the wheat field when compared to the canola field. Three rates of silica solution (SiO₂) representative of amounts that would be found in wheat and canola residues were added to each soil type. High amounts of Si solution and soil Si had a positive effect on soil crust thickness and surface resistance, suggesting that crops high in Si have the ability to contribute to soil crusting. Therefore, it may be beneficial to consider crops with lower amounts of Si when planning crop rotations in areas where soil crusting can be a concern. Further research on this topic will include conducting a field survey on comparable fields this summer.