Calibration of a water content reflectometer and soil water dynamics for an agroforestry practice

Water content reflectometers allow temporal and continuous assessment of spatial differences in soil water dynamics. We hypothesized that volumetric soil water content estimated by the water content reflectometers (CS616 Campbell Sci. Inc., Logan, UT) is influenced by clay content and temperature and therefore site- and or soil-specific equations are required for accurate estimations of soil water. Objectives of the study were to develop calibration equations and to evaluate soil water dynamics for an agroforestry system using the improved calibration equation. Putnam silt loam (fine, smectitic, mesic Vertic Albaqualfs) and Menfro silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalfs) soils were selected with 23–54% clay. Soils were packed in cylinders and sensors were monitored at 5, 10, 15, 20, 25, 30, 35, and 40°C. Calibration equations for volumetric water content (θv) as a function of sensor measured period, temperature, and clay content were developed. Coefficient of determination (r2) and root mean square error (RMSE) were used to compare goodness of fit. RMSE varied between 0.028 and 0.040 m3 m−3 for soil specific and soil-combined linear and quadratic equations with period. Coefficients of determination ranged between 0.89 and 0.96 for these calibrations. RMSE decreased and r2 increased as temperature was included. The effect of temperature varied with water content, with the strongest effect at high water contents. Clay content did not contribute significantly to improve predictability. Water content estimated by the linear calibration equation with period and temperature showed differences in θv influenced by vegetation and soil depth, and closely followed precipitation events and water use by vegetation. The field study showed significant differences between the two treatments. Also the importance of temperature correction is emphasized during periods with large diurnal fluctuations and site specific calibration equations. Results of the study showed that water content reflectometers can be used to estimate θv with less than ±4% error and may need site specific calibration and a temperature correction to research more precise estimates.

[1]  B. Leib,et al.  FIELD EVALUATION AND PERFORMANCE COMPARISON OF SOIL MOISTURE SENSORS , 2003 .

[2]  C. J. Gantzer,et al.  Influence of Grass and Agroforestry Buffer Strips on Soil Hydraulic Properties for an Albaqualf , 2005 .

[3]  Jan W. Hopmans,et al.  Simultaneous Measurement of Soil Penetration Resistance and Water Content with a Combined Penetrometer-TDR Moisture Probe , 2001 .

[4]  Peter P. Motavalli,et al.  Nitrogen losses in runoff from three adjacent agricultural watersheds with claypan soils , 2006 .

[5]  James E. Ayars,et al.  Calibration of Capacitance Probe Sensors using Electric Circuit Theory , 2004 .

[6]  David G. Chandler,et al.  Improved Interpretation of Water Content Reflectometer Measurements in Soils , 2005 .

[7]  H. E. Garrett,et al.  Phosphorus loss and runoff characteristics in three adjacent agricultural watersheds with claypan soils. , 2004, Journal of environmental quality.

[8]  J. Balendonck,et al.  A broad-bandwidth mixed analog/digital integrated circuit for the measurement of complex impedance , 1993 .

[9]  Stephen H. Anderson,et al.  CT-measured pore characteristics of surface and subsurface soils influenced by agroforestry and grass buffers , 2008 .

[10]  D. Or,et al.  Temperature effects on soil bulk dielectric permittivity measured by time domain reflectometry: A physical model , 1999 .

[11]  David G. Chandler,et al.  Field Calibration of Water Content Reflectometers , 2004 .

[12]  J. Ayars,et al.  Calibration of Capacitance Probe Sensors in a Saline Silty Clay Soil , 2004 .

[13]  Julian A. Licata,et al.  Belowground interactions for water between trees and grasses in a temperate semiarid agroforestry system , 2008, Agroforestry Systems.

[14]  J. E. Campbell,et al.  Dielectric properties and influence of conductivity in soils at one to fifty megahertz , 1990 .

[15]  Daniel A. Serrarens,et al.  Soil moisture calibration of TDR multilevel probes , 2000 .

[16]  Gaylon S. Campbell,et al.  Evaluation of simple transmission line oscillators for soil moisture measurement , 1998 .

[17]  P. Ruelle,et al.  Comparison of three calibration procedures for TDR soil moisture sensors , 2003 .

[18]  Jiannong Xin,et al.  Soil Moisture Sensors , 1996 .

[19]  H. Fellner-Feldegg.  Measurement of dielectrics in the time domain , 1969 .

[20]  M. Seyfried,et al.  CALIBRATION OF TIME DOMAIN REFLECTOMETRY FOR MEASUREMENT OF LIQUID WATER IN FROZEN SOILS , 1996 .

[21]  T. J. Dean,et al.  SOIL MOISTURE MEASUREMENT BY AN IMPROVED CAPACITANCE TECHNIQUE, PART I. SENSOR DESIGN AND PERFORMANCE , 1987 .

[22]  H. E. Garrett,et al.  Soil water content and infiltration in agroforestry buffer strips , 2008, Agroforestry Systems.

[23]  Mark S. Seyfried,et al.  Response of a new soil water sensor to variable soil, water content, and temperature , 2001 .

[24]  D. Or,et al.  Time domain reflectometry measurement principles and applications , 2002 .

[25]  H. E. Garrett,et al.  Agroforestry practices, runoff, and nutrient loss: a paired watershed comparison. , 2002, Journal of environmental quality.

[26]  R. Stenger,et al.  Laboratory calibrations of water content reflectometers and their in-situ verification , 2005 .

[27]  Willibald Loiskandl,et al.  Field use and calibration of a TDR-based probe for monitoring water content in a high-clay landslide soil in Austria , 2009 .

[28]  Jeffrey P. Walker,et al.  In situ measurement of soil moisture: a comparison of techniques | NOVA. The University of Newcastle's Digital Repository , 2004 .

[29]  Mark S. Seyfried,et al.  Measurement of soil water content with a 50-MHz soil dielectric sensor , 2004 .