Successive measurement of water retention curves for relativity dry soils using AquaLab VSA

Transcription

1 J. Jpn. Soc. Soil Phys. No. 124, p (2013) AquaLab VSA Successive measurement of water retention curves for relativity dry soils using AquaLab VSA Kunio WATANABE 1, Yurie OSADA 1, Masaru SAKAI 1 and Nobuo TORIDE 1 Abstract: The AquaLab Vapor Sorption Analyzer (VSA) is an automatic isotherm generator to measure water potential for a sample with a chilled-mirror dew-point sensor while gravimetrically tracking the sample weight during wetting and drying processes. In this study, we applied the VSA to measure water retention curves for relatively dry soils ranging from cm to cm, and investigated the accuracy of measurement and properties of the VSA setting parameters. We confirmed that soil water potential was equilibrated with air humidity for the DVS method with 0.01 % h 1 of the weight trigger. The equilibrated water content by weight was almost identical regardless of the soil bulk density since the surface retention was dominant in the dry range. The newly developed DDI (Dynamic Dewpoint Isotherm) method was validated with the DVS method. The DDI method could accurately measure successive retention curves for 50 h measuring time with the flow rate of 100 ml min 1. Hysteretic retention curves as well as scanning curves in a dry range could be also observed in a repeatable manner for Fujinomori silty loam soil, Tokachi Andisol, and Tottori dune sand using the DDI method. Key Words : water retention curve, soil water potential, chilled-mirror dew-point potentiometer, DDI method, hysteresis 1. Decagon WP4 Chilled-mirror dew-point potentiometer 5000 cm Jury and Horton, Graduate School of Bioresources, Mie University, 1577 Kurima- Machiya, Tsu , Japan. Corresponding author Kirkham, 2005; Watanabe et al., 2012 Barbosa-Cánovas et al., 2007; Oliver and Meinders, 2011; Barba et al., 2013 DVS Dynamic Vapor Sorption DDI Dynamic Dewpoint Isotherm DVS DDI Decagon AquaLab VSA Vapor Sorption Analyzer, VSA DDI DVS VSA DVS Shands and Labuza, 2009 DDI DVS Schmidt and Lee, 2009 VSA DDI VSA DVS DDI

2 (2013) h T cm T K P Pa P Pa a w = P/P a w Stokes and Robinson, 1949; Campbell et al., 2010 Kelvin h T Schofield, 1935; Kirkham, 2005 Fig. 1 VSA Schematics of the VSA sample chamber. Fig. 2 WP4 3 Water retention curves for three types of soils measured with hanging water, pressure plate and chilled-mirror dew-point methods. DDI 2. VSA 2.1 Fig. 1 VSA 15 ml 0.1 mg g 37 mm h T = 100 RT ρ w g M lna w (1) R ρ w g M h T h cm 1 25 C a w 0.600, 0.950, h T , , cm 1 a w h T T a w T T ±0.012 C h T ±1000 cm ±0.12 C ±10 4 cm WP4 ±0.01 C 0.1 < a w < < h T < 1000 cm VSA ±0.1 C VSA 0.03 < a w < < h T < cm 2.2 VSA DVS DDI 2 DVS m a w a w T step a step trigger m trig event m trig n trig t max DVS m trig % h 1 n trig m trig m a step m trig n trig a w m m trig t max

3 AquaLab VSA 45 Fig. 3 DVS DDI a a w b m DVS vs. DDI for (a) relative humidity a w and (b) sample weight m as a function of relative time. m trig n trig t max m VSA DDI m a w a w T resolution a w a res Q air t max DDI a res a res a w a res a res = 0.01 DVS DDI VSA DVS DDI 3 VSA 24 % Fig. 2 WP4 ρ b = 1.18 g cm 3 ρ b = 0.95 g cm 3 ρ b = 1.45 g cm 3 van Genuchten 1980 VSA 2 mm ρ b Fig. 1 a w a w ρ b = 0.84 g cm 3 ρ b = 1.18 g cm 3 a w 23 h a w a w h T ρ b 2 g w ρ b θ 3.2 DVS DDI EC 1:5 < 8.5 ms m 1 h T VSA h T h θ h 25 C 25 C Fig. 3 DVS DDI

4 (2013) Fig. 4 m trig t max DVS Water retention curves for Fujinomori silt loam measured with DVS with different trigger m trig and timeout t max. Fig. 5 Q air DDI Water retention curves for Fujinomori silt loam measured with DDI with different flow rate Q air. a w m a w = 0.1 a w = 0.95 DVS a step = 0.1 m trig = 0.01 % h 1 n trig = 3 DDI Q air = 100 ml min 1 t max t max 1 DVS a w m DDI a w m DVS a w m DDI DVS Fig. 4 m trig t max DVS Fig. 3 a w = 0.1 h = cm a w = 0.95 h = cm m trig = 0.01 % h 1 t max θ h = cm θ θ =0.008 m 3 m h m trig 0.1% h h θ =0.002 m 3 m 3 m trig 0.01 % h 1 m trig = 0.01 % h 1 t max = 1 h 10.8 h t max = 0.25 h 5.2 h h θ t max a w = 0.95 θ t max θ h < 10 6 cm θ t max 2 g t max 10 h DVS m m trig = 0.01 % h 1 t max > 10 h t max Fig. 4 Fig. 5 Q air DDI Fig. 3 Fig. 4 Fig. 4 m trig = 0.01 % h 1 t max DVS DDI Q air = 500 ml min 1 θ Q air DVS DDI Q air = 500 ml min 1 49 h Q air = 100 ml min 1 54 h Q air = 25 ml min h Q air = 10 ml min 1 h = cm DDI Q air = 100 ml min Q air = 100 ml min 1 DDI Fig. 6 a a w = 0.1 a w = a w = 0.1 Fig. 6 b a w = 0.95 a w = a w = 0.95

5 AquaLab VSA 47 Fig. 6 DDI a b Scanning curves for Fujinomori silt loam measured with DDI for (a) wetting and subsequent drying, and (b) drying and subsequent wetting. a w a w a w = 0.1 a w = 0.1 a w = 0.95 Fig. 6 a a w = 0.95 a w = 0.1 h = cm Fig. 6 b a w = 0.95 a w = 0.1 a w = 0.95 h = cm DDI Fig. 7 Fig. 6 DDI a w = 0.1 a w = 0.95 Fig. 2 WP4 θ Fig. 7 b 50 h θ = m 3 m 3 θ = m 3 m 3 Israelachvili, 2011 Fig. 7 DDI WP4 a 3 b VSA WP4 (a) Water retention curves for three different soils measured with DDI( ) and a chilled-mirror dew-point method (,, ). (b) Enlargement for the Tottori dune sand.

6 (2013) VSA Fig. 7 b DDI WP4 VSA VSA θ VSA w 2 g VSA g VSA θ w h h < cm Campbell and Gee, 1986; Madsen et al., 1986; Cresswell et al., 2008 h > 10 3 cm h > 10 3 cm h < cm VSA < h < 5000 cm WP4 VSA 4. AquaLab VSA 3 DVS m trig = 0.01 % h 1 DDI Q air = 100 ml min 1 VSA ρ b w ρ b a w a w w ρ b θ DDI 50 h < h < cm DVS DDI DDI VSA Barba, C., Marti, M., Carilla, J., Manich, A.M. and Coderch, L. (2013): Moisture sorption/desorption of protein fibres. Thermochimica Acta, 552: Barbosa-Cánovas, G.B., Fontana, A.J., Schmidt, S.J. and Labuza, T.P. (2007): Water activity in foods. Blackwell Publishing Professional, Ames, IO. Campbell, C.S., Cobos, D.R., Riveras, L.D., Dunne K.M. and Campbell, G.S. (2012): Constructing fast, accurate soil water characteristic curves by combining the Wind/Schindler and vapor pressure techniques, Unsaturated Soils: Research and Applications. pp.55-62, Springer, New York, NY. Campbell, G.S. and Gee, G.W. (1986): Water potential: Miscellaneous methods. In: A. Klute, editor, Methods of soil analysis. Part 1. 2nd ed. Physical and Mineralogical Methods. pp , ASA and SSSA, Madison, WI. Cresswell, H.P., Green, T.W. and McKenzie, N.J. (2008): The adequacy of pressure plate apparatus for determining soil water retention. Soil Sci. Soc. Am. J. 72: Israelachvili, J.N. (2011): Intermolecular and surface forces, 3rd ed. Elsevier Academic Press, Burlington, MA. Jury, W. and Horton, R. (2004): Soil Physics, 6th ed., John Wiley, Hoboken, NJ. Oliver, L. and Meinders, M.B.J. (2011): Dynamic water vapor sorption in gluten and starch films. J. Cereal Sci., 54: Kirkham, M.B. (2005): Principles of soil and plant water relations. Elsevier Academic Press, Burlington, MA. Madsen, H.B., Jensen, C.R. and Boysen T. (1986): A comparison of the thermocouple psychrometer and the pressure plate methods for determination of soil water characteristic. J. Soil Sci., 37: Shands, J and Labuza, T.P. (2009): Comparison of the dynamic dew point isotherm method to the static and dynamic gravimetric methods for the generation of moisture sorption isotherms. IFT annual meeting poster. Anaheim, CA. Schmidt, S.J and Lee, J.W. (2012): Comparison of water vapor sorption isotherms obtained using the new dynamic dewpoint isotherm method to the standard saturated salt slurry method. Food Chemistry, 15: Schofield, R.K. (1935): The pf of the water in soil. pp , Trans. Int. Congr. Soil Sci. 3rd. Oxford, UK. Stokes, R.H. and Robinson, R.A. (1949): Standard solution for humidity control at 25 C. Ind. Eng. Chem., 41: 2013 van Genuchten, M.Th. (1980): A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44:

7 AquaLab VSA 49 Watanabe, K., Takeuchi, M., Osada, M. and Ibata, K. (2012): Micro-chilled-mirror hygrometer for measuring water potential in relatively dry and partially frozen soils. Soil Sci. Soc. Am. J. 76: Yuan, X., Carter, B.P. and Schmidt, S.J. (2011): Determining the Critical Relative Humidity at which the glassy to rubbery transition occurs in polydextrose using an automatic water vapor sorption instrument. J. Food Science, 76: E78 E89. AquaLab VSA 3 VSA cm cm 0.01 % h 1 m trig DVS DDI DVS DDI Q air 100 ml min 1 50 h DDI DDI