Research Estimation Of Plant Root Surface Area By Capacitance Method

In this study,hydroponics and pot experiment were controlled for test.In hydroponic experiments,the tested plants were scindapsus and the roots capacitance were measured in a standard Hoagland nutrient solution.When measuring,a part of upper roots were pulled out the liquid,so there were two part of roots.The roots above liquid level named“above-root”and the roots below liquid level named“below-root”.The roots were marked at liquid level.When roots capacitance measurement completed,the roots were cut into two parts from the mark and roots were weighed and scanned for getting root length,surface area respectively.Analyzed the correlation between characteristic values(length,fresh weight,root surface area)of above-root and below-root and the capacitance measurement value respectively.Results showed that there were significant linear relationship between characteristic values of above-root and capacitance measurement values,but there were no correlation between characteristic values of below-root and capacitance measurement values,means that the liquid shelter the information of roots,caused the information of roots cannot obtain by capacitance method.In order to explore whether soil also shelter the information of roots or not,potted maize was test as object for capacitance measurement.Getting potted soils with different electrical properties by control soil moisture content and soil solution ion concentration at different levels.Analyzed the correlation between root surface area and capacitance measurement in different electrical properties soil and analyzed the influence factors of capacitance test,so as soil impedance characteristics,soil capacitance characteristics,buried depth of soil electrode and excitation frequency of power supply.This paper draws the following conclusions:1.Soil resistance determines if the capacitance method is able to estimate the plant root surface area,soil moisture content,ion concentration affected soil impedance,when the moisture content is 25%and the soil solution was 1000 times dilution Hoagland solution in the soil,and there is significant linear relationship between the measured capacitance value root and root surface area.2.Root characteristic values tested in the soil by capacitance method,equation as Y=kX+b can be used to simulate the relationship between capacitance value and root surface area,the coefficients“k”of the equation controls by the power excitation frequency,when excitation frequency was raised,the value of k would decrease;constant term b value is affected by soil capacitance characteristics,soil electric capacitance decreased when the frequency of excitation power supply increased.When the excitation frequency is greater than or equal to 1 k Hz,the influence of soil capacitance on measurement results could be neglected,and the soil could be seen as pure conductors in the test circuit.Soil impedance is less affected by frequency.3.With the soil electrode penetration depth increases,the measured soil capacitance value increases correspondingly,and the measured root capacitance is basically unchanged.4.When the excitation frequency is 100,120,1K,10K and 100k Hz,the coefficient of determination R~2 between the root capacitance and the root surface area are 0.65,0.658,0.666,0.65 and 0.556,respectively.It is recommended that the excitation frequency of the 1 kHz be selected as the appropriate frequency of the test.Study on influencing factors of estimating plant root area table based on capacitance method,in order to regulate the application operational approach of capacitance method,and provide references to promote the application of the capacitance method on estimating root area in practice.