Research conducted in the Brazilian Amazon indicates that carbonized materials, such as charcoal, are responsible for the persistent fertility of anthropogenic soils known as Terra Preta. In the present study, we compared the effect of Flash Carbonized macadamia nutshell charcoal with 22.5% volatile matter (VM) content on vegetable crop yield and soil chemical properties of a degraded Andisol and a highly weathered Ultisol. We conducted three greenhouse experiments with treatments of varying charcoal rates, lime, mineral fertilizers, organic amendments, and mixtures. In the Andisol, charcoal showed no beneficial effect on plant growth, and we observed a negative effect of charcoal at the highest rates. Charcoal did not improve plant uptake of P, K, and Ca, whereas N and Mg uptake significantly decreased at the highest rate of charcoal. Charcoal increased soil pH and total organic carbon, but cation exchange capacity (CEC) decreased with increasing rates of charcoal. In the Ultisol, treatments receiving charcoal did not show any improvement in plant yield compared to soils treated with mineral fertilizers and lime. These results conflict with previous findings which demonstrate that charcoal has a beneficial effect on crop growth and soil properties in highly weathered tropical soils. This discrepancy may be due to the high VM content of Flash Carbonized charcoal used in the experiment, which may explain the detrimental effect on plant growth. Our findings suggest that the type of charcoal and its VM content may affect its suitability as a soil amendment. We are currently conducting a greenhouse experiment using macadamia nutshell charcoal with a 6.3% VM content, and results will be available by the date of the presentation.