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In Situ Comparison of Three Dielectric Soil Moisture Sensors in Drip Irrigated Sandy Soils

Danish Institute of Agricultural Sciences, Department of Agroecology, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark

View larger version (17K): [in a new window]   Fig. 1. Installation of TDR and CS616 sensors in drip irrigated potatoes. In (a) experimental plots at Jyndevad Research Station, and (b) Jyndevad soil and (c) Foulum soil in the semi-field basins at Research Centre Foulum. Position of mother tubers and drip points is shown as well.

View larger version (22K): [in a new window]   Fig. 2. Measurements of volumetric water content from vertically installed CS616 sensors in the Jyndevad soil in the lysimeter at Research Centre Foulum. FC, field capacity (50 hPa); WP, wilting point (15500 hPa).

View larger version (28K): [in a new window]   Fig. 3. Measurements of volumetric water content from horizontally sensors (TDR and CS616) installed in a depth of 15 cm in the lysimeter at Research Centre Foulum: (a) Jyndevad soil, (b) Foulum soil, (c) Rønhave soil.

View larger version (14K): [in a new window]   Fig. 4. New calibration of the CS616 sensor for (a) Jyndevad soil, (b) Foulum soil, (c) Rønhave soil. Mean values (n = 3) of VWC measured by the TDR sensors are plotted against mean values (n = 3) of VWC measured by the CS616 sensors. Error bars indicate ± 1 standard deviation.

View larger version (22K): [in a new window]   Fig. 5. Volumetric water content measured with the CS616 sensor using the standard calibration and VWC measured with TDR at Jyndevad Research Station (left y axis). Differences between TDR calculated from mean values of the CS616 and TDR measurements are shown at the top of the figure (right y axis). The differences are shown for both the manufacturer's standard calibration and the new calibration. FC, field capacity (50 hPa); WP, wilting point (15500 hPa). For precipitation and irrigation amounts, see Fig. 8.

View larger version (124K): [in a new window]   Fig. 6. Photos of CS616 sensors centered above a mother tuber at the time of potato maturity in the Jyndevad soil at Jyndevad Research Station.

View larger version (30K): [in a new window]   Fig. 7. Comparison between TDR sensor and the calibrated CS616 sensor from the basins in the semi-field facility at Research Centre Foulum: (a) Jyndevad (Jyndevad W1), (b) Jyndevad (Jyndevad W2), (c) Foulum (Foulum W1). FC, field capacity (50 and 100 hPa in Jyndevad soil and Foulum soil, respectively); WP, wilting point (15500 hPa). Black dots indicate dates of fertigation (Table 2).

View larger version (19K): [in a new window]   Fig. 8. Measured volumetric water content by the Aquaflex sensor and TDR sensors installed in Jyndevad soil at Jyndevad Experimental Station. FC, field capacity (50 hPa); WP, wilting point (15500 hPa). The right y axis shows both precipitation and irrigation.

View larger version (31K): [in a new window]   Fig. 9. Comparison of volumetric water content between TDR sensor and Aquaflex sensor controlled by the user supplied data logger from the Jyndevad basin (Jyndevad W2) in the semi-field facility at Research Centre Foulum.