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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVED WATER RESOURCES MANAGEMENT FOR IRRIGATED AGRICULTURE IN THE PACIFIC NORTHWEST Title: Use of time domain reflectometry for continuous monitoring of nitrate-nitrogen in soil and water

Authors
item Payero, J - UNIVERSITY OF NEBRASKA
item Tarkalson, David
item Irmak, S - UNIVERSITY OF NEBRASKA

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2005
Publication Date: September 1, 2006
Citation: Payero, J.O., Tarkalson, D.D., Irmak, S. 2006. Use of time domain reflectometry for continuous monitoring of nitrate-nitrogen in soil and water. Applied Engineering in Agriculture. 22(5):689-700.

Interpretive Summary: Nitrate-nitrogen losses to ground and surface water are an environmental and agronomic concern in modern crop production systems. Monitoring techniques for nitrogen use in agricultural production are needed to increase crop yield, optimize nitrogen use, and reduce nitrate-nitrogen leaching. Time domain reflectometry could potentially be calibrated to continuously measure nitrate-nitrogen in soil and water. This study was conducted in North Platte, NE to evaluate the use of time domain reflectometry for continuous monitoring of nitrate-nitrogen in soil and water. Temperature of the medium, solute concentration, cable length, and volumetric soil water content all influenced the bulk electrical conductivity sensed by the time domain reflectometry probes. In the field, measured soil nitrate-nitrogen related well with values estimated using time domain reflectometry. These results indicated that time domain reflectometry, if properly calibrated for a particular soil, could be used to continuously monitor nitrate-nitrogen in soil, and should also be well-suited for monitoring nitrate-nitrogen in groundwater and surface water.

Technical Abstract: Nitrate-Nitrogen (NO3-N) losses to ground and surface water are an environmental and agronomic concern in modern crop production systems in the Central Great Plains. Monitoring techniques for nitrogen use in agricultural production are needed to increase crop yield, optimize nitrogen use, and reduce NO3-N leaching. Time domain reflectometry (TDR) could potentially be calibrated to continuously measure NO3-N in soil and water. The objectives of this study were to: (1) evaluate the effect of different factors affecting the response of the bulk electrical conductivity (ECb) sensed by TDR, (2) compare the sensitivity and differences between vertically-installed and horizontally-installed probes for measuring NO3-N leaching in the soil profile, and (3) evaluate the feasibility of using TDR to measure changes in NO3-N concentration in an irrigated agricultural soil. Studies were conducted in the laboratory and in the field at the University of Nebraska West Central Research and Extension Center in North Platte, Nebraska. Temperature of the medium (Ts), solute concentration, TDR cable length, and volumetric soil water content all influenced and were linearly related to the bulk electrical conductivity (ECb) sensed by the TDR probes. In the field, measured soil NO3-N correlated well with values estimated using TDR measurements of ECb, corrected for changes in volumetric soil water content and Ts. These results indicated that TDR, if properly calibrated for a particular soil, could be used to continuously monitor NO3-N in soil, and should also be well-suited for monitoring NO3-N in groundwater and surface water. It is, however, important to perform the calibration over a long enough period of time to include the expected range of volumetric soil water content, Ts, and NO3-N values to obtain adequate accuracy.

Last Modified: 12/22/2014
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