Assessing the role of enhanced weathering in sustainable agriculture : benefits and risks for crop growth in a temperate climate
Rijnders, J. 2005.
Abstract
The Industrial Revolution initiated a rapid increase in atmospheric greenhouse gas concentrations, primarily driven by fossil fuel combustion. This accelerates climate change through global warming, resulting in more frequent and severe weather events. To mitigate these effects, global leaders aim to limit warming to below 2C, and preferably 1.5C, relative to pre-industrial levels. This requires not only reducing greenhouse gas emissions but also implementing active carbon dioxide removal (CDR) strategies. Enhanced weathering (EW) is a promising CDR technique involving the application of ground silicate minerals to terrestrial surfaces, where they react with CO2 and water, storing carbon for millennia. Aside from its CDR potential, EW offers agronomic benefits by increasing soil pH, cation exchange capacity (CEC), alkalinity, and nutrient availability, potentially enhancing crop performance. Most research has focused on EW's CDR potential, while its effects on crop productivity are less studied, especially in temperate climates. Moreover, the role of soil biota in accelerating weathering processes remains underexplored. This thesis investigates the impact of EW on crop growth, nutrient cycling, and heavy metal dynamics in a temperate climate using mesocosm experiments. It also examines the influence of different silicate materials, grain sizes, precipitation regimes, and the role of soil organisms, specifically earthworms and arbuscular mycorrhizal fungi (AMF). Results show that EW improved soil pH, CEC, and nutrient availability, especially Ca, Mg, and Si. However, no significant changes were observed for N, P, or K, likely due fertilization at the beginning of each growing season. Consequently, biomass responses were limited, even though plant concentrations of Ca, Mg, and Si increased. Enhanced Si uptake suggest the potential of EW to improve a plant's drought resilience, but effects varied with material type and grain size. Additionally, earthworms improved nutrient availability and uptake by plants, while AMF showed limited effects, potentially due to fertilization, reducing the plant's dependence on AMF symbiosis, and because of the short experimental duration. EW also increased availability of heavy metal species that were abundant in the applied silicate material, while other heavy metal species decreased due to the increase in soil pH. Although increased heavy metal availability resulted in accumulation in the plant roots, concentrations generally did not increase in the aboveground plant parts, and even decreased in some cases. In conclusion, EW holds promise for sustainable agriculture, but careful material selection, application management, and integration with other sustainable agricultural practices are essential to optimize benefits and minimize environmental risks.
