The quantification of heavy metals is crucial to many different applications, and particularly relevant to agriculture. Here we describe an electrochemical sensor to detect and quantify ultra-low concentrations of aluminum in solutions. High aluminum levels are associated with inadequate crop development, growth, and production. To this end, we demonstrate and validate a cheaper glassy carbon electrode modified by the electrochemical reduction of bismuth in an acetate buffer, for square wave voltammetry (SWV) of Al3+ in a cupferron solution 0.22 mmol L−1 + ammonium sulfate buffer 0.4 mmol L−1 pH 5.50, using double-potential pulse chronoamperometry. The proposed method ensures reproducible and stable surface modification of the electrode, and a sensor with linear response in the concentration range of 1.85×10−10 to 3.70×10−6 mol L−1 with a detection limit of 0.025 ppb and resistance to interfering metals such as lead (Pb) cadmium (Cd) and zinc (Zn). This type of technology is amenable to industrial scaling and production and could be used for soil characterization and remediation in agriculture, as well as other applications related to food production and safety where accurate and rapid, yet cost-effective, on-site monitoring is required.