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Soil Water Content Determination by Karl Fischer Titration

Department of Soil Science, North Dakota State Univ., P.O. Box 5638, Fargo, ND 58105

*Corresponding author (prunty{at}plains.nodak.edu).

ABSTRACT

Karl Fischer (KF) titration is a specific analysis for water content. We hypothesized that it may be useful in soils where volatiles besides water are present, since oven drying (OD) determines total volatile components, not water content specifically. We examined KF titration as a technique for soil water content determination. Two soils (a quartz sand separate and Barnes loam [fine-loamy, mixed Udic Haploboroll]) were prepared with varying known amounts of water (0–240 g kg^–1) and a non-aqueous-phase liquid (NAPL), either octane or toluene (0–128 g kg^–1), then analyzed for water content using both the OD and KF methods. The experimental matrix included all six possible combinations of two soils x three liquids. Soil water contents determined by the calibrated KF method (w_c) compared favorably to those determined by OD (w_o). Slopes for the six w_c vs. w_o regressions ranged from 0.980 to 1.009 while intercepts ranged from –0.6 to 7.8 g kg^–1. Mean r² was 0.97 with a range of 0.93 to 0.99. The sand with octane and sand with toluene mixtures had intercepts of 6.1 ± 2.5 and 7.8 ± 5.4 g kg^–1 (95% confidence intervals), respectively. All other intercept confidence intervals included zero. Plots of the data show essentially a 1:1 correspondence of w_c to w_o. Variability was greater when toluene was present, possibly because of toluene's higher vapor pressure.

Contribution of the North Dakota Agric. Exp. Stn.

Received for publication September 9, 1996.