The root activities of castor bean plants can change the soil around their roots, affecting how copper (Cu) is distributed. When Cu was added to the soil, the concentration of Cu in the plant parts increased significantly. In the soil near the roots, the type of Cu changed, becoming more available for plants to take up. The pH of the soil decreased, while the levels of nitrogen and carbon increased. Also, the amount of simple organic acids and amino acids in the soil near the roots increased, making Cu more available for plants to use.