Carbonatite rock can enhance plant growth and nutrition depending on crop traits

The increasing global demand for sustainably-produced crops has led to a renewed interest in exploiting unprocessed rocks as soil amendments and fertilizers. Carbonatite rocks are of particular relevance because of their rapid weathering rates and diverse nutrient contents. However, there are insufficient data to support or refute their efficacy and to understand their mechanism(s) of action. Here, the effects of a carbonatite on two crops were assessed and compared to those of calcitic lime. Wheat and pea were repeatedly grown under a low-nutrient regime under greenhouse conditions and their development, biomass, and shoot nutrient content were measured. The effect of the carbonatite on soil CO2 evolution was also tested for wheat. Wheat grown with carbonatite produced 40% more shoot biomass and 50% more root biomass than plants grown with lime. There was a sharp reduction in specific root length (SRL), consistent with approximately 60% increases in shoot contents of N, P, K, and Mn. These effects were smaller for pea. For wheat, CO2 from the soil was 70% greater with lime than with carbonatite. We conclude that carbonatites can provide benefits to plants beyond serving as liming agents. In addition, root architecture and SRL appear to be useful traits for predicting plant responsiveness to carbonatite addition.