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and its Simulation along with the Determination of the Thermal Conductivity Alhan SARIYEV, Ergin ÇELEBİ, Metin MÜJDECİ University of Çukurova, Faculty of Agriculture, Department of Soil Science, Balcali/Adana/Turkey Abstract Soil temperature was studied in soil columns at steady and unsteady flow conditions at 4 different moisture content rates. Changes in temperature in soil columns were determined both with sensors and mathematical models. AD/DA converter cards and sensors were determined to be sensitive for measuring external heat sources. Thus, AD/DA converter cards and sensors are suitable for utilising in soil temperature studies. Moreover, mathematical models are also determined to be in accordance with measured results. Introduction Soil temperature significantly effects plant growth, at 0-5 oC, germination and root development can not be healthy, moreover, below freezing point, biological activity stops. Each plant requires specific heat levels for growing, since chemical reactions, micro organism activity, aeration, water holding and movement are all heat dependant parameters. Soil colour, specific heat, water content, soil surface relief, type and intensity of vegetation cover are effectiveness soil heat (Yeşilsoy, 1975). Recent, studies plant growth revealed models are that successfully used and applied in agricultural sciences. Plant growth models, based on blocks principle, all parameters should be individually outlined and correlated with suitable software. Soil head is an important parameter in block based modelling of Energy-Mass and plant growth of currently developing Agro ecosystem studies (Poluektov, 1991). Theory Mathematical modelling and digital analyses of soil temperature is an important approach. When mathematical modelling of soil temperature is evaluated at 2 conditions, for unsteady flow limit and initial condition can be expressed as flow (Poluektov, 1991).  Higher and lower limits can be respectively expressed as follows; Higher limit condition:  İnitial condition: Ti (x) = f (x) In Eq. (1),  is the volume heat capacity related to soil moisture content,  soil heat conductivity, T (0C) ; soil temperature, t (hour) ; time, x (cm); thickness of the soil layer, N- soil depth. Other parameters are, Ta, air temperature, n: cloud cover, u: wind speed,  relative air moisture.Equation expressed above is defined below ( Sarıyev et al, 1998):  For simplifying this expression, determination of temperature in homogenous soil can be expected as follows;  As seen in this equation, for any J layer temperature surface and sub layer temperature and layer position are in relation to each other, whereas NR is the number of layers. For testing the approaches (steady and unsteady conditions) in both condition experiment were undertaken is soil columns, and probable similarities were investigated. Data were stored in computers by utilising AD/DA converter card and sensors. Materials and Methods The physical and chemical properties of disturbed and undisturbed soil samples collected from the Experimental Farm of Field Crops Department, University of Çukurova were determined according to the following methods. Texture Bouyoucos (1951), Bulk density on undisturbed soil samples collected by 100 cc cylinders (Blake&Hartge1986), Hydraulic conductivity (Klute&Dirksen,1986), Salinity (U.S. Salinity Laboratory Staff, 1954), pH and %CaCO3 equivalent (Schlichting and Blume, 1966) (Table 1). Methods employed are; Properties heat of Analog / Digital (A/D) converters used for measuring. Data collectors' capability of data storage and capacity let the use of varying methods. With the aid of the software, data-collecting system collects data via suitable modules or sensors. For heat measurements, Super (output impedance 2K ohm) 14 byte AD/DA card is used in computer, capable of converting data to digital data, which were attained 16 different points. Analog data can be calculated less than 2 ms by sensors. Measurement and Experiment Set The experiment set consists 2 soil columns, and each column 8 sensors were placed in. Temperature changes were observed in one column by using varying moistures. Also, for determining the sensitivity of the sensors 500W and 100W heat sources were utilized. Soils were placed in plastic columns (R=11 cm) and kept in field conditions. Holes are opened at 10 cm intervals in columns and heat sensors were placed in to the holes. Changes in temperature and periodic measurements were transferred to computer. Software was developed for the use and calibration of A/D card. Temperature values were calibrated and analysed in MS Excel software. The valid equation, trend and validity values were observed for each channel. These trends were also used for temperature the measurement program. The height of PVC column is 1 m with a radius of 5.25 cm, having 10 layers with 10 cm thickness with soil of known bulk density (Figure 1). 
Results Physical and Chemical Properties of Soils are given in Table.1.  Measurement values and results obtained from the model are given in Figure 2,3.  In equation (1), the thermal conductivity and the heat capacity can be measured by using finite differences method and  ( Hanks and Ashcroft, 1985) equation respectively as in the following formula: in the equation T 31 and T 11 are same layer,  initial and final temperature in certain period, T1 and T2 represents adjoining layer temperatures and  is the thickness of the layer The heat conductivity were calculated by taking into account moisture (Q=%33.5) and low moisture (Q=%15) conditions along with measured values. The heat conductivity value for the moisture conditions were higher than low moisture contents of the soil,  Temperature changes due to external heat resource application are given in figure 5 at moisture condition.  Results and Discussion 2 different methods were utilised for the determination of temperature values in soil columns. In the first method, values were obtained using the Analog-Digital (AD/DA-14 byte) card, connected to 16 different sensors. The card converter sensored temperatures to digital data in relation to time and depth. In the second, the advanced step of the study, the simulated soil temperature related to time and depth were also measured using the mathematical model developed in this work. Basic physical laws, soil temperature capacity and flux values along with initial soil moisture were the main components of the model. Methods used in this study both yielded satisfactory results. However, there are negligible differences between measurement and model values. These differences have occurred due to the continuous evaporation of the soil moisture from the surface of the soil, which is effective on soil temperature. Also, balancing the parameters according to the constant moisture content in the model has been the main factor causing the difference. Mean difference in other layers is relatively low and well correlated. Thus, in similar soil temperature studies the use of suggested method will yield satisfactory results. Results revealed that AD/DA converter card and sensors are determined to be sensitive for measuring the effect of external heat sources. Thus, AD/DA converter card and sensors can be successfully used for measuring other physical and chemical properties of soils when they are effectively calibrated. References . Blake, G.R.,& Hartge, K.H.,1986. Bulk Density In: Methods of Soil Analysis, Part 1, Physical and Mineralogical Methods. (Ed: A. Klute) Agr. Monogr. 9. ASA and SSSA, Madison WI.p.363-375. . Bouyoucos, G.J., 1951. Hydrometer Method Improved For Marking Particle Size Analysis of Soils. Agronomy J. 54, pp: 464-465. . Hanks, R., J., Ashcroft, G., L., 1985. Applied Soil Pyysics. Springer- Verlag, 151p. . Klute, A., & Dirksen, C., 1986. Hydraulic Conductivity and Diffusivity: Laboratory Methods. In: Methods of Soil Analysis, Part1, Physical and Mineralogical Methods. (Ed: A. Klute) Agr. Monogr. 9.ASA and SSSA, Madison WI p. 687-734. . Poluektov, R .A. 1991. Simulation of Agroecosystem Dinamics. Gidrometoizdat, St-Petersburg, 312 p. . Sarıyev, A., Aydın, C.,& Yusufova., M.1998. Measurement and Modelling of Heat Distribution by Computer Based Termometers in Soil Columns M. Şefik YEŞILSOY International Symposium on Arid Region Soil, p.336-344, Menemen, İzmir, Turkey. . Schlichting, E., & Blume, E., 1966. Bodenkundliches Practikum. Verlag Paul Parey. Hamburg and Berlin. U.S., Salinity Laboratory Staff, 1954. Diagnosis and Improvement of Soil Saline and Alkaline Soils. Agricultural Handbook No:60. . Yeşilsoy, M.Ş., 1975. Measurement of Soil Temperature conductivity according to Soil Properties TUBİTAK V. Scientific Conference. |