Electrical Conductivity Method for Measuring Concentrations of Diammonium Hydrogen Phosphate and Potassium Chloride in Their Mixed Solution

Abstract

【Background】Integrating fertilization and irrigation is a potential agricultural management technology and its success depends on accurately real-time monitoring the change in fertilizers concentration. The existing electric conductivity (EC) method is only able to detect concentration of single fertilizer, and developing simple and cheap device to accurately real-time monitor concentration of mixed fertilizers solution is hence needed. 【Objective】The purpose of this paper is to study the feasibility and accuracy of an electric conductivity method to real-time monitor the concentrations of diammonium hydrogen phosphate and potassium chloride at in their mixed solution. 【Method】We first measured the EC of the mixture of diammonium phosphate and potassium chloride at different concentrations ranging from 2 g/L to 10 g/L and different temperatures ranging from 20 ℃ to 45 ℃, and then analyzed the change in EC with temperature, concentration and ratios of the two fertilizers using the grey correlation analysis (GRA). 【Result】The EC of the mixed solution increased with its concentration and temperature and decreased as the ratio (n) of diammonium hydrogen phosphate to potassium chloride increased. It was also found that the factors affecting the EC of the mixed solution was ranked in the descending order of concentration > temperature > n. Based on goodness of the fitting, the evaluation index of the GRA was compared with the measured data after cubic spline interpolation and cubic B-spline interpolation, from which we obtained pairwise models for concentration-EC, temperature-EC and n-EC relationships, respectively. These enabled us to derive a model to predict the concentration of each fertilizer in their mixed solution based on EC, temperature, and the ratio n. 【Conclusion】Testing against measured data showed that the model accuracy was 97.53%, meeting the requirement in practical application. The method can thus be used for real-time monitoring concentration of mixed fertilizers solution in integrated irrigation and fertilization.

Keywords

• mixed fertilizers
• electrical conductivity
• concentration measurement
• grey correlation model