Assessing Errors and Accuracy in Dew‐Point Potentiometer and Pressure Plate Extractor Meaurements. Issue 1 (14th December 2012)

• Record Type: Journal Article
• Authors: Gubiani, Paulo Ivonir; Reichert, José Miguel; Campbell, Colin; Reinert, Dalvan José; Gelain, Neiva Somavilla
• Is Part Of: Soil Science Society of America Journal. Volume 77:Issue 1(2013)
• Page Start: 19
• Page End: 24
• Publication Date: 2012-12-14
• Subjects: Soils -- United States -- Periodicals; Soil science -- Periodicals; Periodicals; 631.4973
• DOI: 10.2136/sssaj2012.0024
• Languages: English
• ISSNs: 0361-5995

Abstract

Abstract : Soil water potential can be determined quickly with a WP4 device, which uses a chilled mirror dew point technique. The instrument can be used to check the soil water potential of samples drained in a porous plate extractor (PPE). However, soil water potential measured in both devices on the same soil sample may not be in agreement, mainly in the wet‐end of the water retention curve. This work investigates this problem, and further evaluates how equilibrating soil samples in a PPE with different permeable material at the sample bottom (filter paper [FP], polyester fabric [PE], and synthetic knitwear [SK]) affects the final water potential. Soil samples (soil fraction <2 mm) of an Ultisol and an Oxisol were drained at 0.5 and 1.5 MPa pressure in a PPE and the water potential of these samples was measured in a WP4. Another fraction of the same soil was used to obtain a WP4 water retention curve. The permeable materials caused large differences in water retention at 0.5 MPa pressure (0.006 g g −1 in the Oxisol and 0.021 g g −1 in the Ultisol), and the FP allowed more water drainage than PE and SK, indicating the latter two should be avoided when using a PPE to determine water extraction. In both soils, the water potential measured in the WP4 was lower than −0.5 MPa for samples under 0.5 MPa pressure and greater than −1.5 MPa for samples under 1.5 MPa pressure. The increase of residual (fitted minus measured) in the WP4 water retention curve indicated that above −0.7 MPa the precision of WP4 measurements decreased drastically.