Tractor with fertilizer spreader next to a pile of rock fertilizer

Fatima Haque, Rafael M. Santos, and Yi Wai Chiang. 2020. CO2 sequestration by wollastonite-amended agricultural soils – An Ontario field study. International Journal of Greenhouse Gas Control. doi:10.1016/j.ijggc.2020.103017
Aashvi Dudhaiya, Fatima Haque, Hugo Fantucci, and Rafael M. Santos. 2019. Characterization of physically fractionated wollastonite-amended agricultural soils. Minerals. doi:10.3390/min9100635
Research summary by Hugo Fantucci

key messages

  • Wollastonite is a natural calcium silicate mineral present in Ontario that can be used as an agricultural soil amendment
  • Amending soil with wollastonite can increase inorganic carbon content in soils, thus potentially being another carbon sequestration solution
  • Agricultural fields in Southern Ontario demonstrated carbon sequestration potential, which was found to be around 0.2T of CO2 per tonne of wollastonite applied in this study

Every growing season, farmers apply mineral fertilizers on their fields to improve soil fertility and crop health. Some locally mined minerals, such as wollastonite, can naturally react with carbon dioxide (CO2) gas. This reaction can capture carbon from the atmosphere, and permanently store it in the soil in the form of stable inorganic molecules known as carbonates. This approach may give us another tool to curb climate change and sequester carbon in the soil.

The mineral wollastonite is a certified organic soil remineralizer, primarily composed of calcium silicates, and mined in Ontario. When added to soil, wollastonite reacts with CO2 dissolved in water to produce calcium carbonate, thus sequestering carbon. The main purpose of this research was to evaluate the behaviour of wollastonite as a soil amendment in agricultural fields. In these studies, researchers measured how much carbon was captured in soil over time: up to three field applications over three years, at 1 to 5 tonne ha-1 in different commercial field crops (soybean, leafy vegetables and potato) in Ontario, Canada.

What they found

Across the three commercial farms, applying wollastonite to agricultural fields increased soil inorganic carbon content by 63-89%. Within 12 to 36 months after application, 2.35 to 6.05 tonne CO2 ha-1 were sequestered in a vegetable cropping system, respectively. This indicates that the storage potential of wollastonite is 0.20 tonne of CO2 sequestered per tonne of wollastonite, and the storage rate is 0.08 tonne CO2. ha-1 month-1.

Although not measured directly, one participating farmer reported that wollastonite application also improved potato growth. By boosting plant resilience, the farmer also saw the potential to reduce insect attack thanks to the plant-available silica from wollastonite. This would be an interesting avenue for future research.

Why it matters

Inorganic carbon is different than soil organic matter (and organic carbon). While it does not directly affect soil health, there are potential benefits. Sequestering carbon by applying wollastonite as a soil amendment has potential to benefit both farmers and the broader society by helping to mitigate climate change. In the future, farmers may be able to claim carbon credits for this practice via a growing number of private carbon markets established in recent years.

How they did it

Three separate commercial-scale fields near Paris, Alliston, and Woodstock, Ontario, Canada, were sampled. Wollastonite was applied in field-length strips with different application methods: on the potato farm, wollastonite was broadcast with a lime spreader in the Fall; on the soybean farm, wollastonite was broadcast before planting; on the leafy vegetable farm, wollastonite was applied at the end of May and incorporated (6-7 inches). Soil cores (6”) were randomly collected to obtain 100 cores per field/plot, and characterized by the Agriculture and Food Laboratory Services (Guelph, Canada) and the research team at University of Guelph, in order to determine the soil type, and carbonate (inorganic carbon) content.

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