<p>The use of organic amendments, such as biochar, can reduce the uptake of lead (II) ions (Pb²⁺) by plant roots, thus alleviating lead toxicity in various crops. This study first investigated the adsorption capacity of Pb²⁺ by coffee grounds biochar (CGBC) and arginine-modified CGBC (A_CGBC) in an aqueous solution. The result confirms that arginine-modified coffee grounds biochar (A_CGBC) is highly effective in adsorbing Pb²⁺ from aqueous solutions and reducing lead availability in soils. The enhanced adsorption capacity of 142.75&#xa0;mg·g⁻¹ for A_CGBC, compared to 38.92&#xa0;mg·g⁻¹ for unmodified CGBC, can be attributed to nitrogen and oxygen functional groups that coordinate effectively with Pb²⁺ ions. Computational studies further supported these findings, demonstrating that the modified biochar surface exhibited strong ion–dipole interactions, leading to better Pb²⁺ binding. When applied to soil, A_CGBC successfully reduced the Pb²⁺ levels in Sangyod rice planting pots. The addition of 2% A_CGBC decreased lead content in the soil, roots, and grains by 20%, 30%, and 85%, respectively, highlighting its potential as a sustainable soil amendment. These findings A_CGBC is potential as an eco-friendly, sustainable solution for reducing heavy metal uptake in crops.</p>