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Sensors 2016, 16(8), 1239; doi:10.3390/s16081239

Soil Water Content Sensor Response to Organic Matter Content under Laboratory Conditions

College of Agriculture and Human Sciences, Prairie View A&M University, Prairie View, TX 77446, USA
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Author to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Received: 30 June 2016 / Revised: 26 July 2016 / Accepted: 29 July 2016 / Published: 5 August 2016
(This article belongs to the Section Physical Sensors)
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Abstract

Studies show that the performance of soil water content monitoring (SWCM) sensors is affected by soil physical and chemical properties. However, the effect of organic matter on SWCM sensor responses remains less understood. Therefore, the objectives of this study are to (i) assess the effect of organic matter on the accuracy and precision of SWCM sensors using a commercially available soil water content monitoring sensor; and (ii) account for the organic matter effect on the sensor’s accuracy. Sand columns with seven rates of oven-dried sawdust (2%, 4%, 6%, 8%, 10%, 12% and 18% v/v, used as an organic matter amendment), thoroughly mixed with quartz sand, and a control without sawdust were prepared by packing quartz sand in two-liter glass containers. Sand was purposely chosen because of the absence of any organic matter or salinity, and also because sand has a relatively low cation exchange capacity that will not interfere with the treatment effect of the current work. Sensor readings (raw counts) were monitored at seven water content levels (0, 0.02, 0.04, 0.08, 0.12, 0.18, 0.24, and 0.30 cm3 cm−3) by uniformly adding the corresponding volumes of deionized water in addition to the oven-dry one. Sensor readings were significantly (p < 0.05) affected by the organic matter level and water content. Sensor readings were strongly correlated with the organic matter level (R2 = 0.92). In addition, the default calibration equation underestimated the water content readings at the lower water content range (<0.05 cm3 cm−3), while it overestimated the water content at the higher water content range (>0.05 cm3 cm−3). A new polynomial calibration equation that uses raw count and organic matter content as covariates improved the accuracy of the sensor (RMSE = 0.01 cm3 cm−3). Overall, findings of this study highlight the need to account for the effect of soil organic matter content to improve the accuracy and precision of the tested sensor under different soils and environmental conditions. View Full-Text
Keywords: capacitance sensor; 10HS sensor; organic matter; sensor precision; sensor accuracy capacitance sensor; 10HS sensor; organic matter; sensor precision; sensor accuracy
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MDPI and ACS Style

Fares, A.; Awal, R.; Bayabil, H.K. Soil Water Content Sensor Response to Organic Matter Content under Laboratory Conditions. Sensors 2016, 16, 1239.

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