Low-cost Soil Moisture and EC Sensor Design for Soil Salinity Assessment

Abstract

Soil salinization is one of the major land degradation problems affecting about 932 million hectares (Mha) in the World, and about 6.74 Mha in India. Since soil salinization affects the plant growth which affects agricultural production and food security, it needs to be monitored and managed well. The existing field devices for assessing soil salinity are expensive (> US${\$}$ 150 for the sensor alone). So, a lowcost sensor (about US70) has been designed for assessing soil salinity by measuring soil moisture and electrical conductivity (EC). The device uses oscillation frequency shift technique for measuring soil moisture, and electrical resistivity is used for bulk EC measurement. The sensor prototype has been designed and tested using downward infiltration method with 14 soil samples. Regression models have been developed for soil moisture estimation from frequency measurements. Pore water EC has been estimated from bulk EC measurements for determining soil salinity. The regression models developed for soil moisture estimation from frequency has R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ranging from 0.92 - 0.95, which is significant for accepting the models. The bulk EC measurements were transformed to pore water EC, and a threshold regression model has been developed from for determining soil salinity at different moisture levels. The threshold pore water EC regression model has an R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 0.74, which is acceptable for determining salinity from pore water EC values.