Use of Capacitance Sensors for Continuous Monitoring of Nitrate Content in Soil

Abstract：Continuous monitoring of nitrate in soil is needed to optimize nutrient management and reduce nitrate leaching.Both laboratory and field calibration experiments were conducted to quantify the relationship between nitrate content in soil and soil bulk electrical conductivity,water content and temperature monitored by capacitance sensors.In laboratory experiment,seven soil container tests were conducted with varying injection concentrations of ammonium nitrate ranging from 0 to 10 g/L.Also Soil bulk electrical conductivity,water content,and temperature were continuously monitored during the growing seasons of spring corn drip irrigated at different levels in 2009 and 2010.The results showed that the bulk electrical conductivity could reflect the dynamics of nitrate content in soil.The relationship between soil nitrate content and soil bulk electrical conductivity,water content and temperature could be described by a quadratic polynomial.All of the three parameters monitored by the capacitance sensors had significant effects on nitrate content in soil（P≤0.01）.In situ calibration was recommenced by this study to improve the prediction accuracy of nitrate content in soil as the accuracy of the regression polynomial was influenced by many factors,such as initial soil nutrients,salt contents and spatial variability.