Chemical and mineralogical assessment of the wollastonite-amended agricultural soils - an Ontario field study

摘要

Global mean temperature has increased as a result of human-induced activities, and there is a pressing need to curb the annually increasing atmospheric concentration of CO_2. Terrestrial enhanced weathering is the spreading of silicate rock powder on land, and can help to sequester CO_2 through carbonation of calcium- and magnesium-rich minerals. Agricultural land covers 37% of the Earth's land surface and it offers a natural sink for atmospheric CO_2 as pedogenic carbon. Application of wollastonite (mainly CaSiO_3) to the soil has the potential to boost the capacity of this carbon pool, as it can lead to the accumulation of inorganic carbon as carbonate minerals. Wollastonite has been commercialized in Ontario as a soil amendment for several years, but it is not known if or how much CO_2 it is sequestering in agricultural soils. In the present study, wollastonite-amended soil was collected from three different fields located in Ontario: a farm growing lettuce, kale, romaine, etc., in Paris (Field 1); a potato farm in Alliston (Field 2); and a soybean farm in Woodstock (Field 3). The main aim of this study was to conduct chemical and mineralogical assessments of these soils to determine their carbonate content and the fate of the wollastonite. The soils were tested for pedogenic inorganic carbon content using calcimeter and TGA analysis, and XRD and SEM-EDX analyses were performed to detect differences in mineral composition between wollastonite-amended soil and untreated control. In the Field 1, the pedogenic inorganic carbonate was the highest (0.68 %CaCO_3) in case of soil amended thrice with wollastonite, which was 2.6 times higher than the soil with a single application. Similarly, for the soil from the Fields 2 and 3, calcimeter and TGA analysis confirmed the accumulation of pedogenic inorganic carbonate compared to control. Mineralogical analysis of the amended soils showed the presence of additional polymorphs of SiO_2, which may originate from the wollastonite after dissolution of calcium. It has been concluded that amending agricultural soils with wollastonite is an effective geoengineering tool that has the potential to permanently store carbonates and mitigate atmospheric CO_2 levels.