Soil and plant cations as affected by application of wood ash, biochar, and papermill biosolids

Recycling woody biomass for application to croplands is one option to divert materials from landfills and simultaneously improve degraded soil properties. Considering the diversity of materials that vary widely in characteristics, an understanding of the comparative effects of a single or combined application of these byproducts is missing with regards to soil C accumulation and availability of base and metallic cations. A field study was conducted in Québec City, QC, Canada, to assess the effects relative to untreated control of wood ash (10 and 20 Mg dry wt. ha⁻¹), pine biochar (10 Mg dry wt. ha⁻¹), papermill biosolids (12 Mg PB dry wt. ha⁻¹), and a combination of wood ash and PB on soil C, pH, and cations in a circumneutral loamy soil. The site was cropped to a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation. All materials were applied before corn planting and the effects of treatment were followed over two growing seasons. Applying wood ash resulted in the statistically largest increases (p < 0.01) in soil pH, percentage base saturation, and Mehlich-3 K, Ca, Mg, Zn, and Cd. Wood ash also increased K concentration in straw and total K accumulation for both plants, but its effect on plant metallic cations was limited. With a single application, PB only increased Mehlich-3 Ca with no further effect when combined with wood ash, while pine biochar was limited to sequester soil C. Therefore, this study indicated that wood ash could benefit a corn–soybean rotation by enhancing soil quality and crop yield.