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

Abstract

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 (h v ) as a function of sensor measured period, temperature, and clay content were developed. Coefficient of determination (r 2 ) and root mean square error (RMSE) were used to compare goodness of fit. RMSE varied between 0.028 and 0.040 m 3 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 r 2 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 h v 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 h v with less than ±4% error and may need site specific calibration and a temperature correction to research more precise estimates.

Evaluations of the effects of soil properties and electrical conductivity on the water content reflectometer calibration for landfill cover soils

“…Western and Seyfried (2005) reported the WCR to be significantly influenced by temperature at high water contents. Similar results can be found in Stangl et al (2009) and Udawatta et al (2011). Francesca et al (2010 and Arsoy et al (2013) confirmed that WCRs were impacted by bulk electrical conductivity and temperature to a greater extent than by dielectric relaxation.…”

Root distribution and water use in coffee shaded with Tabebuia rosea Bertol. and Simarouba glauca DC. compared to full sun coffee in sub-optimal environmental conditions

“…Undisturbed soil samples of sufficient dimensions to insert a TDR probe were also extracted from each soil layer (two samples per layer). Progressive drying was measured simultaneously by TDR and by weighing, so that a calibration equation was available for each soil layer, following a protocol adapted from Udawatta et al (2011). The volumetric soil water contents were then multiplied by the thickness of the soil layers in which each TDR probe was inserted to calculate the soil water content of each layer.…”

Laboratory temperature-compensating calibration procedure for soil water content determination by reflectometry

“…Others factors may influence on period measurements by means CS616 sensor, especially the clay content (Udawatta et al, 2011;Ojo et al, 2015). We observed that the soil moisture instrument calibrations developed by the manufacturers for a general proposing are not always adaptable for use under field conditions.…”

“…The procedures in this work were adapted by the methods proposed by Benson & Wang, (2006) and Udawatta et al (2011). At the experimental field of UNEMAT, Tangará da Serra Campus, deformed soil samples were collected at November of 2016, in subsequent layers: 0.0-0.2 and 0.2-0.4 m to represent the soil profile.…”