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United States Department of Agriculture

Agricultural Research Service

Title: Repeatability of Soil Apparent Electrical Conductivity Measured by a Coulter Sensor

Authors
item Jabro, Jalal "jay"
item Evans, Robert
item Stevens, William
item Iversen, William

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2007
Publication Date: January 1, 2008
Repository URL: http://hdl.handle.net/10113/10719
Citation: Jabro, J.D., Evans, R.G., Stevens, W.B., Iversen, W.M. 2008. Repeatability of soil apparent electrical conductivity measured by a coulter sensor. Soil Science. 173(1):35-45.

Interpretive Summary: This study evaluates the repeatability of the coulter sensor by comparing ECa data from two passes in barley stubble at two 1.6-ha sites, one with a sandy loam soil texture (Nesson) and the other a clay loam soil texture (EARC). Sampling points in the direction of travel were approximately 1.45 m apart for both passes. The ECa measurements from both passes were compared at shallow (0-30 cm) and deep (0-90 cm) soil depths. Both CV and RMSE results indicated less agreement and more variations in ECa measurements between the two passes at shallow depths than deep depths. The repeatability was evaluated by calculating a 95% confidence interval for the difference between ECa measurements of the two passes against their mean. This method was more informative than the identity relationship method for comparing repeated measurements. Based on the evaluation criterion used in this study, the results demonstrate marginally acceptable repeatability between the two passes at shallow depth and acceptable repeatability at deep depths at both fields. The lack of agreement between pass1 and pass2 in ECa measurements at shallow depths could have resulted from soil disturbance and compaction caused by the coulter sensor during pass1 process. The variation between pass1 and pass2 could also be attributed to the roughness of soil surface during pass1 compared with a smoother surface during the pass2 mapping process. Generally, the results indicate that the on-the-go EC sensors can be useful and provide reliable data for describing field spatial variability in precision farming.

Technical Abstract: Repeatability of a measurement can be assessed by characterizing the variation between successive measurements of the same quantity. Apparent electrical conductivity (ECa) measured using an on-the-go coulter sensor offers advantages for mapping soil variability because detailed data can be colleted easily and inexpensively using on-the-go EC sensors; however, there has been little research investigating the repeatability of these sensors. The objective of this study was to evaluate the repeatability of the coulter sensor by comparing ECa data from two passes in barley stubble at two 1.6-ha sites, one with a sandy loam soil texture (Nesson) and the other a clay loam soil texture (EARC). Sampling points in the direction of travel were approximately 1.45 m apart for both passes. The ECa measurements from both passes were compared at shallow (0-30 cm) and deep (0-90 cm) soil depths. The CVs of ECa measurements for shallow and deep depths from pass1 were higher than those from pass2 at both sites. The root mean square error (RMSE) values of ECa measurements between pass1 and pass2 at shallow and deep depths for the Nesson site were 0.76 and 0.51, respectively, while, the RMSE for the EARC site were 4.06 and 2.93 at shallow and deep depths, respectively. The repeatability was evaluated using a 95% confidence interval for the difference between ECa measurements of the two passes. Results demonstrate marginally acceptable repeatability between the two passes at shallow depths and acceptable repeatability at deep depths. The reasons for lack of agreement between pass1 and pass2 in ECa measurements at shallow depths could have resulted from soil disturbance and compaction caused by the coulter sensor during pass1 process. Regardless of discrepancies for shallow depths, the results indicate that the on-the-go ECa sensors can be useful and provide reliable data for describing field spatial variability in precision farming.

Last Modified: 8/29/2014
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