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United States Department of Agriculture

Agricultural Research Service

Title: Passive capillary sampler for measuring soil water drainage and flux in the vadose zone: Design, performance and enhancement

Authors
item JABRO, JALAL "JAY"
item Kim, Yunseop
item Evans, Robert
item IVERSEN, WILLIAM
item STEVENS, WILLIAM

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 14, 2008
Publication Date: September 1, 2008
Repository URL: http://hdl.handle.net/10113/23068
Citation: Jabro, J.D., Kim, Y., Evans, R.G., Iversen, W.M., Stevens, W.B. 2008. Passive capillary sampler for measuring soil water drainage and flux in the vadose zone: Design, performance and enhancement. Applied Engineering in Agriculture. 24(4):439-446.

Interpretive Summary: Twelve automated PCAPs with sampling surface dimensions of 31 cm * 91 cm and 87 cm in height were designed, constructed, and placed 90 cm below the soil surface in a Lihen sandy loam soil we demonstrated and evaluated the utility, performance and accuracy of an automated PCAP fluxmeter we designed for in-situ continuous measuring and estimating of drainage water and fluxes in the vadose zone. Our enhanced PCAPS design has a significantly enlarged surface capture area (2700 cm2) compared with other PCAP fluxmeters. It employs an automated datalogger to transmit data simultaneously to a remote host by means of Bluetooth sensing technology. This design allows real-time monitoring and estimating of drainage water and fluxes as it extracts soil pore water. Automation allows our PCAP sampler to operate without the need for costly and time-consuming supportive systems such as vacuums and pumps. We found excellent statistical agreement between the extracted and logged drainage water fluxes, with R2 ranging between 0.96 and 0.99. Our results also confirmed that our PCAP design provides a reliable, accurate and convenient means to measure water drainage and fluxes in the vadose zone. In the course of field testing over the last year we incorporated several additional enhancements, all of which we recommend for optimal performance.

Technical Abstract: Various soil water samplers are used to monitor, measure and estimate drainage water, fluxes and solute transport in the soil vadose zone. Passive capillary samplers (PCAPs) have shown potential to provide better measurements and estimates of soil water drainage and fluxes than other lysimeters and field sampling methods. Twelve automated PCAPs with sampling surface dimensions of 31 cm * 91 cm and 87 cm in height were designed, constructed, and placed 90 cm below the soil surface in a Lihen sandy loam (sandy, mixed, frigid Entic Haplustoll). The PCAPs were installed to continually quantify the amount of drainage water and fluxes occurring below the rootzone of sugarbeet (Beta vulgaris L.) and malting barley (Hordeum vulgare L.) cropping system under 30 mm (low replacement) and 15 mm (high replacement) irrigation frequencies. Two TDR sensors were positioned above each PCAP to monitor soil water contents and gradients continuously. Drainage water was extracted, collected and measured periodically (weekly from May to Mid-August, fortnightly until late September and monthly thereafter until Mid-November) and samples were stored for further analysis. This design incorporated Bluetooth sensing technology to enable an automated datalogger to transmit drainage water and flux data simultaneously every 15 minutes to a remote host. Real-time seamless monitoring and measuring of drainage water and fluxes was thus possible without the need for costly time-consuming supportive operations. Our novel PCAP design provided an accurate and convenient way to measure water drainage and flux in the vadose zone. Moreover, it offered a significantly larger coverage area (2700 cm2) than similarly designed vadose zone fluxmeters or PCAPs. In the course of field testing over the last year we incorporated several additional enhancements, all of which we recommend for optimal performance.

Last Modified: 8/19/2014
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