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The Role of Drop Volume and Number on Soil Water Repellency Determination
Author(s) -
Hallin I.,
Douglas P.,
Doerr S.H.,
Bryant R.
Publication year - 2013
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2013.04.0130
Subject(s) - soil water , drop (telecommunication) , infiltration (hvac) , soil science , penetration (warfare) , environmental science , standard deviation , organic matter , chemistry , mathematics , materials science , statistics , composite material , telecommunications , organic chemistry , operations research , computer science
The water drop penetration time (WDPT) test is commonly used to evaluate the persistence of soil water repellency by placing water drops on the soil surface and recording the time to complete infiltration. Currently no standard protocol exists regarding the number or volume of drops applied, and often neither detail is provided when WDPT is reported. This study evaluated how mean WDPT (WDPT M ) varies with drop volume and the number of drops required to obtain WDPT M within a given precision. Two naturally water‐repellent soils were tested with 416 drops each of 15, 20, 80, and 200 μL. Wettable analogs of each soil were prepared and combined with the repellent soils to create various soil mixtures, to which 20‐ and 200‐μL drops were applied. The WDPT M was found to vary significantly (α = 0.05) with drop number and volume, and the relationship likely depends largely on soil heterogeneity from variations in particle size, organic matter content, and the distribution of hydrophobic compounds within the soil. The results of this study support the following recommendations: (i) a reliable WDPT M (±10%) can be obtained with 95% confidence from 30 drops of 80‐ to 200‐μL size (smaller drops can be used but will reflect microtopographical variability as heterogeneity increases); and (ii) water repellency class can be determined with 95% confidence from six drops and with 90% confidence from one drop, regardless of volume. Standard deviations should always be included to give some indication of the heterogeneity of water repellency within the soil.