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Gypsum Moisture‐Block Calibration Based on Electrical Conductivity in Distilled Water
Author(s) -
Tanner C. B.,
Abrams E.,
Zubriski J. C.
Publication year - 1949
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/sssaj1949.036159950013000c0009x
Subject(s) - citation , library science , distilled water , soil water , computer science , environmental science , chemistry , soil science , chromatography
O WISCONSIN'S 35 million acres there are about 5 million acres of tillable land where water supply is frequently the limiting factor in plant growth. Of these 5 million acres there are about 2 million acres that have water readily available for irrigation. In 1947, the University of Wisconsin began extensive use of gypsum blocks for supplemental irrigation control and for obtaining moisture data necessary for the interpretations of yield data on fertility plots and on variety trials. For this field work, three soil-moisture availability levels of the soil must be known: (a) first permanent wilting percentage, (b) field capacity, (c) the soil moisture tension at which irrigation should be applied. Because of the way block resistance varies with moisture content when emplaced in the soil, Bouyoucos and Mick (3) suggest that block resistance ranges of 75,000 ohms or greater and 450 to 650 ohms are satisfactory indications of first permanent wilting percentage and moisture equivalent, respectively. Also suggested is a resistance of 11,000 ohms, or slightly higher, as a practical indication of need for supplemental irrigation. Field work done at Wisconsin agrees generally with these findings. Satisfactory use of these general ranges to indicate first permanent wilting percentage, field capacity, and time for water application requires that resistance values of all the blocks be within reasonably close agreement of each other for any given level of soil moisture availability. Consequently, either there must be some test for block uniformity over the moisture range, so that blocks may be discarded if not within a prescribed tolerance or the individual blocks must be calibrated so that resistance of each block is known' for any moisture availability. Bouyoucos and Mick (3) state that "A convenient test for uniformity is to measure the resistance of the blocks when immersed in distilled water. Resistances between 450 and 440 ohms at 70° F are considered satisfactory." The present study was undertaken to test further the resistance readings of gypsum blocks' when saturated in distilled water as an indication of block uniformity from saturation to moisture tensions at first permanent wilting percentage.