Investigating the electrical properties of soil as an indicator of the content of the NPK element in the soil

Abstract

This study aims to analyze the correlation between electrical properties of soil and NPK concentration in the soil. The conductivity and capacitance of soil with various NPK concentrations were measured. The main contribution in this study is to provide recommendations on the use of the corresponding electrical parameters for determining NPK levels in the soil. So far, the measurement of the electrical method generally uses the conductivity value for all conditions, even in wet and dry soil conditions. In fact, wet and dry soil conditions affect the conductivity. Therefore, other electrical parameters are needed that can correct the results of NPK measurements in the soil. Conductivity in relation to capacitance can show better measurement validity. In this study, the linearity of the relation between conductivity or capacitance to the addition of NPK levels in the soil was investigated. Soil samples were prepared by varying the mass concentrations of the elements N, P, and K separately. The conductivity and capacitance values for each NPK variation were measured and mapped. The results showed that the conductivity in dry soil conditions was more linear, with average coefficient of determination of the three elements being 0.81, compared to capacitance with a coefficient of determination of 0.72. Whereas the addition of water to the soil sample resulted in better sensitivity and linearity in the capacitance compared to the conductivity, with each average coefficient of determination being 0.55 and 0.34. These results provide alternative solutions using capacitance as an indicator for determination of NPK content in wet soil. The use of capacitance parameters combined with conductivity in determining NPK content in soil is a novelty contribution to this research and can be applied to the measurement technology in agriculture.