ARS | Publication request: Performance evaluation and accuracy of passive capillary samplers (PCAPs)for estimating real-time drainage water fluxes

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 28, 2012
Publication Date: August 14, 2012
Citation: Jabro, J.D., Iversen, W.M., Evans, R.G. 2012. Performance evaluation and accuracy of passive capillary samplers (PCAPs)for estimating real-time drainage water fluxes. Applied Engineering in Agriculture. 18(4):537-542.

Interpretive Summary: We evaluated the performance and accuracy of automated passive capillary wick samplers (PCAPs) for in-situ continuous estimation of drainage water below the rootzone of a sugarbeet-potato-barley rotation under two irrigation frequencies using five years of data. The drainage water recorded by the datalogger from the tipping bucket was compared with the manually extracted drainage water using several statistical methods. An excellent agreement exists between the extracted and logged drainage water volumes with r values equal to 0.943, 0.959, 0.990, 0.943, 0.949, and 0.954 for 2006, 2007, 2008, 2009, 2010 and five years combined, respectively. The RRMSE values were 81, 49, 16, 58, 72, and 62% and EF values were 0.889, 0.914, 0.975, 0.885, 0.901, and 0.907 for 2006, 2007, 2008, 2009, 2010, and 5-yr combined, respectively. Small differences existed between drainage volumes recorded by the datalogger from the tipping buckets and extracted drainage volumes by pump. The cause of discrepancies between logged drainage water and water that was measured manually could have resulted from human sampling error and mechanical operational problems with the PCAPs under field conditions. Overall, statistical results indicated that our automated PCAP samplers performed well, were accurate and able to continuously monitor and estimate drainage water volume and flux in the vadose zone without the need for alternative costly and time-consuming sampling methods.

Technical Abstract: Successful monitoring of pollutant transport through the soil profile requires accurate, reliable, and appropriate instrumentation to measure amount of drainage water or flux within the vadose layer. We evaluated the performance and accuracy of automated passive capillary wick samplers (PCAPs) for in-situ continuous estimation of drainage water below the rootzone of a sugarbeet-potato-barley rotation under two irrigation frequencies using five years of data. Twelve automated PCAPs with outside sampling surface dimensions of 91 cm length x 31 cm width x 87 cm height were placed 90 cm below the soil surface in a Lihen sandy loam. The drainage water recorded by the datalogger from the tipping bucket was compared with the manually extracted drainage water using several statistical methods. The relative root mean square values (RRMSE) were 81, 49, 16, 58, 72, and 62% and logging efficiency (EF) values were 0.889, 0.914, 0.975, 0.885, 0.901, and 0.907 for 2006, 2007, 2008, 2009, 2010, and 5-yr combined, respectively. Overall, statistical results indicated that our automated PCAP samplers performed well and were accurately able to continuously monitor and estimate drainage water volumes and fluxes in the vadose zone without the need for costly and time-consuming supportive methods. Slight variations between the extracted and logged drainage water volumes may have resulted from human sampling error and mechanical operational problems with tipping buckets and PCAP assembly. Keywords: Irrigation, drainage, lysimeter, performance, vadose zone.