Vol. 1, No. 2 Journal of Agricultural Science 42 Measurement of Dielectric Behavior of Fertilized Soil at Microwave Frequency Vivek Yadav, Anil Kumar, Sudeep Sharan & AK Sinha Gyrotron Laboratory, Central Electronics Engineering Research Institute (CEERI) Pilani 333031, India E-mail: vivek.ceeri@gmail.com; aksinha@ceeri.ernet.in M Yadav, VK Gupta & RA Jangid Microwave research laboratory, Raj Rishi Collège, Alwar 301001, India Abstract The paper presents the experimental results which have been carried out for understanding the behavior of solid dielectrics in the form of soil at microwave frequency and check the dielectric and electric response of some fertilizers in soil in presence of microwave energy. A simple and rapid measurement method (two point method) was used to determine the dielectric constant at microwave frequency. The microwave beam generated by microwave source was reflected by the dielectric sample which was placed in rectangular waveguide and fundamental mode was considered. The microwave source reflection klystron of frequency range of X- band was used. The soil samples were prepared by mixing different concentrations of some fertilizers in soil. The soils were taken from ‘Behror Alwar (RAJ)’ and different fertilizers ‘Urea, Shree Ram-33, Shree Ram-50P, D.A.P., Mosaic’ were taken from market. Keywords: Dielectric constant, Dielectric loss, a.c. conductivity, Relaxation time, Reflection, Two point method 1. Introduction The behavior of dielectric materials in presence of electromagnetic (EM) field is entirely different from that in presence of direct current field. In order to understand the behavior of dielectric materials under the action of electromagnetic fields, one has to investigate its interaction in such EM field. In the presence of an alternative electric field, the dielectric materials get polarized along the field direction. The degree of polarization depends upon the applied EM power and the nature of material itself (1). The static dielectric constant and dipole moment values are the measure of the polarization of the material at low frequencies. However, presence of high frequency field, there exist a time lag in the attainment of equilibrium in system with the changing field and hence an anomalous dispersion (dielectric constant decrease within increase in frequency) takes place. This in turn gives rise to the dielectric relaxation. Spatial and temporal variation of the moisture content in the surface layer of soil is considered important in agriculture. Its knowledge is important for the sowing, development, successful maturation of a crop along with rainfall runoff prediction agricultural yields forecasting and boundary layer heat exchange for meteorological and climates studies(2). The different percentage of fertilizer content in the soil gives rise to a large variation in the dielectric constant. Thus, the knowledge of the variation of dielectric constant of the soil at different fertilizer content is necessary for the efficient use of soil. 1.1 Role of porosity in soil fertility Porosity of the soil greatly helps to judge the moisture movement within the soil. Macro pores allow readily movement of air and water. It does not hold water under normal condition. In contrast, macro pores can hold more water and restrict the movement of air and water in soil. Thus, in sandy soil, inspite of the low total porosity, the movement of air and water is surprisingly rapid because of the dominance of the macro pore spaces. Porosity of soil is easily changed. Any operation that reduces aggregation and decreases the amount of organic matter in the soil, decreases pore space(3). In the present work, dielectric constants of the loamy sand soils with different concentration of different fertilizers content and fixed moisture content were measured at fixed frequency 9.8 GHz in the laboratory condition. 2. Material and method The two-point method of measuring dielectric constant is used for the measurements of dielectric properties. An X-band microwave bench operating at 9.8 GHz in the TE10 mode with slotted section was used and the shift of minima is needed