Instant and Mobile Electrochemical Quantification of Inorganic Phosphorus in Soil Extracts

Abstract

Phosphorous (P) is critical for food production and is vital to both plant and animal life. Measurement and management of soil P are crucial for soil fertility maintenance and optimum plant growth while reducing P losses from agricultural fields and improving downstream water quality. Several costly and time-consuming analytical methods provide offsite P analysis, while onsite sensor-based P analysis method shows the potential to provide fast and cost-effective P measurements. This study presented a portable electrochemical adaptation of the Environmental Protection Agency (EPA) recommended colorimetric method for measuring inorganic P. In this research, cyclic voltammetry was used to quantify inorganic P in the range between 0.25 and 3.08 mg · l−1 (typical soil P range). The limit of detection achieved was 0.18 mg · l−1. Other common ions did not interfere with P detection and confirmed P selectivity. Unlike the EPA recommended method, this method only required molybdate ions as the complexing agent. Processed soil samples in the laboratory were used to validate this method against inductively coupled plasma optical emission spectroscopy. This method showed an average recovery of 98.27% of P, highlighting its suitability for field P measurements. The proposed electrochemical approach is promising for low-cost, simple, and portable infield soil P tests.