Effects of silicon on soil crusting and soil quality

Taylor Lynn-Marie Beard

Silicon (Si) levels have a wide range of variation in plant and soil systems depending on abiotic and biotic factors. In the inland Pacific Northwest the predominant cropping system relies on wheat (a Si accumulator). Within this region, studies have shown high levels of total soil Si and evidence of Si compounds becoming potential cementing agents therefore degrading soil quality. The dependence of Si cycling on plant type, environmental factors, and agronomic inputs needs to be assessed in order to determine if introduction of canola (a non-accumulator of Si) could enhance soil quality by reducing the occurrence or severity of soil crusting in comparison to wheat-dominated systems. Both wheat and canola were grown in a greenhouse and upon harvest the wheat residue accumulated between 40–65% more Si than canola. This residue was then used in a laboratory incubation with soil pH as a variable. The results suggest that a higher pH, rather than residue type, was the primary factor positively affecting surface resistance, water soluble Si (Siws), and amorphous Si (Siam). The greenhouse residues were also used in a decomposition study, which showed wheat had a slightly faster decomposition rate compared to canola, consistent with the lower starting C:N ratio of the wheat residue. An additional incubation with applications of amorphous silica (SiO2) confirmed that such applications positively influence water loss, soil Si, surface resistance, and crust thickness. In addition to the silica treatments, soils from two cropping systems were used: one previously cropped in wheat and the other in canola. The soil previously cropped in wheat had higher soil Siam, surface resistance, and crust thickness compared to the canola system demonstrating the influence crop rotation can have on Si related soil properties. A field survey of Siws, Siam, and surface resistance showed little dependence across cropping systems. As shown from the experiments under controlled conditions, it can be concluded that Si cycling does affect important soil physical properties. The lack of confirmation in the field survey suggests that other factors influence the state of Si in active cropping systems and should be the focus of further research.

Effects of silicon on soil crusting and soil quality

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