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چكيده انگليسي :

Effect of Soil Moisture and Porosity on Ultrasonic Waves Student s Full Name Mojtaba Kashi Alashti E mail address m alashti@ag iut ac ir Date of Submission April 2011 Department of Agricultural Machinery Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor s Names and E mail addresses A Esehaghbeygi Assist Prof esehaghbeygi@cc iut ac irAbstract Soil physical characteristics have main role for plant growing and product efficiency Soilphysical measurement is necessary to correct management and exploitation of soil and bestoperation Soil moisture content and its porosity are important physical factors to growing plants Soil with appropriate moisture and porosity obtain better conditions for plant growing To predictsoil moisture and its porosity the methods with advantages and disadvantages were recommended Ultrasonic nondestructive tests have high ability for estimate soil physical characteristics becauseultrasonic waves need a medium for transmission Ultrasonic tests used in agricultural products indifferent frequencies but used in soil rarely In the present study the characteristics oftransmission ultrasonic waves in the soil sample with two transducers transmitter and receiver intwo frequencies 75 kHz and 125 kHz and two levels of voltage 900Vp p and 1800Vp p wereinvestigated To estimate soil moisture content and porosity the velocity and attenuation of waveswas measured Soil samples in three levels of porosity 55 47 and 40 and three soil texturesclay clay loam and sandy loam in many levels of soil moisture was used Soil moisture contentbased on the dry weight was used from high plastic limit and continued to a constant ratio in theoven Moisture range was 30 12 for clay 24 5 7 for clay loam and 19 6 d b forsandy loam soil Soil sample rings had 69 mm in diameter and 20 mm in thickness Soil samplesfixed in a holder and the transducers was put in its two sides Soil samples included twotransducers were put in the oven at 55 and at each 15 minute intervals the velocity andattenuation of ultrasonic waves and the weight of control sample were measured To study soiltexture effect dry soil samples with 40 mm in thickness and 40 in porosity was used Analysisof variance with complete randomized design showed significant difference in soil texture porosity and moisture for wave velocity and its attenuation The frequencies of 75 kHz and 125kHz had significant effect on the wave velocity and attenuation in addition different levels ofvoltage had significant effect on the attenuation The attenuation increased with increasing soilporosity The attenuation had direct relation with moisture content in all soil texture and porosity and increased with increasing moisture content The attenuation increased with increasing sandpercent in all soil texture and the levels of soil porosity and its moisture in addition the velocityinversed attenuation The velocity of waves had inversed relation on soil moisture and itsporosity in other word velocity of transmitted waves decreased with increasing soil moisture andporosity Received signals for 75 kHz transducer was stable and uniform compare to the 125 kHzin addition the attenuation was low Received signals for voltage 1800Vp p was better than900Vp p Voltage had significant effect on the attenuation but no effect on the velocity All soilfactors texture porosity and moisture content had significant effect on the velocity andattenuation of ultrasonic waves but the velocity was in an obvious manner Keywords Ultrasonic wave Soil texture Moisture Porosity

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