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Some Freezing Point Depression Measurements on Cores of Soil in Which Cotton and Sunflower Plants Were Wilted
Author(s) -
Richards L. A.,
Campbell R. B.,
Healton L. H.
Publication year - 1950
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/sssaj1950.036159950014000c0011x
Subject(s) - sunflower , citation , principal (computer security) , agriculture , mathematics , library science , horticulture , archaeology , geography , computer science , biology , operating system
S I N C E the early measurements of Bouyoucos and McCool (2), numerous workers have used cryoscopic methods for studying the physical condition of moisture in soil. In particular, freezing point measurements have been made to evaluate the condition of soil moisture at the wilting point. For most of this work, an experimental curve for the relation of freezing point to moisture content has been plotted for a given soil and the freezing point corresponding to the wilting percentage has been obtained from the curve by interpolation. Schofield and DaCosta (13), from freezing point measurements on seven soils, found that pF ranged from 4.0 to nearly 4.34. Converting to equivalent negative pressure or soil moisture stress, this corresponds to a range of from 10 to approximately 21.2 atmospheres. Bodmar. and Day (1) likewise obtained the freezing-pointdepression for seven soils at the wilting percentage and calculated moisture potential values ranging from -10.3 to -22.0 X 10 ergs/gm. This corresponds to a stress range from 10.2 to 21.7 atmospheres. Robertson and Kohnke (12) obtained freezing-point-depression values on 20 samples of Indiana soils at the wilting-percentage and calculated pF values ranging from 4.0 to 4.28. This corresponds to a stress range from 10 to 19 atmospheres. Veihmeyer and Hendrickson (14) give freezing point curves from which the interpolated freezing points at the permanent-wilting-percentage for 5 of the soils range from -0.7 to -1.8° C. This corresponds to a stress range from 8.4 to 21.7 atmospheres. It is known that the freezing-point-depression depends somewhat on the state of packing of the soil. The present paper reports freezing point measurements on soil cores taken from cans in which plants were grown to a wilted condition. The method of taking the samples and making the freezing measurements has been described by Richards and Campbell (11). The soils used in the experiment range in texture from fine to coarse and are listed in Table 1. The moisture retaining properties of the soils are indicated by the 15-atmospherepercentages and the saturation percentages listed in the table. The electrical conductivity of the saturation extract and the freezing-point-depression of the saturation extract are given in columns 3 and 4. All of the soils are from the western part of the United States and contain'some soluble salts. Soils 57, 63, and 314 as obtained from the field were too saline to permit good growth of test plants, so these samples were leached. The data in Table 1 represent the condition of the soils as they were used in the wilting tests and as used in these tests only the Reagan clay loam, No. 85, contained enough soluble salt to be rated as a saline soil. The last column of the table gives calculated values of the osmotic pressure of the soil solution at the 15-atmosphere-percentage. In making the calculation it was assumed that both the total amount and the ionization of the soluble salts in solution were the same at the 15atmosphere-percentage and the saturation percentage. The figures therefore are higher than would be found during moisture depletion by plants, but indicate an upper limit for the value of the osmotic pressure at or near the wilting condition for the various soils.