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.

A Novel Paper-Based Reagentless Dual Functional Soil Test to Instantly Detect Phosphate Infield

“…The CV approach used in this study was based on our previous work [14]. The phosphate ion in the dissolution medium reacted with acidic molybdate (AMT) released from the ERR IFP, forming a complex Keggin phosphomolybdate anion [14,32].…”

“…The phosphate ion in the dissolution medium reacted with acidic molybdate (AMT) released from the ERR IFP, forming a complex Keggin phosphomolybdate anion [14,32]. The observed anodic and cathodic peaks (Figure 6a) are due to the two steps of reduction reaction (Equations ( 2) and ( 3)) and corresponding oxidation reactions [14,33]. phate ion in the dissolution medium reacted with acidic molybdate (AMT) released from the ERR IFP, forming a complex Keggin phosphomolybdate anion [14,32].…”

“…The correlation between P extracted by chemical extractant and the P amount available to the plants is necessary towards selecting the right chemical extractant [12]. PAP is extracted from soil samples using different chemical extractants that require lengthy extraction time, agitation, and sample filtration [13] and is subsequently detected using inductively coupled plasma optical emission spectroscopy (ICP) and colorimetric tools [14][15][16][17] to assess soil P needs. However, these detection tools are accompanied by many challenges such as extensive maintenance, high annual consumption costs, complicated steps, requirement of trained personnel, immobility, and lengthy analysis time [14][15][16][17].…”

“…PAP is extracted from soil samples using different chemical extractants that require lengthy extraction time, agitation, and sample filtration [13] and is subsequently detected using inductively coupled plasma optical emission spectroscopy (ICP) and colorimetric tools [14][15][16][17] to assess soil P needs. However, these detection tools are accompanied by many challenges such as extensive maintenance, high annual consumption costs, complicated steps, requirement of trained personnel, immobility, and lengthy analysis time [14][15][16][17]. and Olsen [19] are two chemical extractants that are widely used in soil analysis laboratories to extract labile PAP and have consistently shown a good correlation with P uptaken by plants [20][21][22].…”

“…In this proposed method, Mehlich-3 components, along with P detection reagents, were impregnated in filter papers to extract P due to its high selectivity towards P extraction and its ability to extract P in a short period [18] (5 min extraction) as opposed to other P extractants which require longer extraction times. In our previous study, our team developed an electrochemical method for inorganic soil P determination in Olsen P extractants based on anodic oxidation of phosphomolybdate [14,29]. However, this method could not be deployed in infield P detection because it requires safe disposal of the extractant solution chemical wastes.…”