H. TschinkelH. Tschinkel is an FAO Watershed Management Specialist working at the Tunisian National Forest Research Institute in Ariana (Tunis).
The author gives a simple, practical method for measuring soil moisture stress, shows when it may be usefully applied, and summarizes some recent writings on the subject.
The measurement of soil moisture content, as well as the force with which moisture is held by the soil, is an important aspect of watershed management and hydrology. The assessment of this force, commonly referred to as soil moisture stress, is essential for meaningful interpretations of the soil moisture used by plants. Unfortunately, the lack of a simple method of measurement has been a serious obstacle for hydrologists and those involved in watershed management. It is my purpose here to summarize a recently improved method for measuring soil moisture stress through the use of filter papers and to list some of the applications, since these are quite scattered in hydrology writings.
McQueen and Miller (1966, 1968) revived and improved a method described by Gardner in 1937, which measures the soil moisture tension based on the amount of water ate-sorbed by filter paper in contact with a soil sample. Apparently independently, Fawcett and Collis-George (1967) tested an almost identical method and came to very similar conclusions. The procedure for the method described by McQueen and Miller is as follows:
A soil sample is extracted and placed in a soil sample can. A disc of a particular brand of filter paper is placed in contact with the sample and the can hermetically sealed with plastic tape. The can is then stored at 20°C for two to three weeks during which time the filter paper reaches moisture equilibrium with the soil. The paper is removed from the can, and its moisture content put against a calibration curve gives the moisture stress of the soil sample in bar or in pF units. The degree of moisture can be easily obtained, and the only expensive item of equipment, an analytical balance, is available in most laboratories.
There are two applications of this method:
1. It may be applied to measure the moisture stress of a particular point in the soil at a particular time. Thus, Branson, Miller and McQueen (1965, 1970) used soil moisture stress measurements to help explain the distribution of plant communities in two arid regions of the United States. Herrmann (1970, 1971) studied the water balance and variations in moisture stress under several vegetation formations in tropical mountains. Miller (1969) used the method to study changes in soil chemistry due to drainage of water through the soil. McQueen and Miller (1972) measured soil moisture content and stress under riparian vegetation in order to describe mechanisms of moisture retention and migration. I used the method (Tschinkel, 1972a, 1972b) to determine whether high soil moisture: stress during the dry season might explain the poor growth of Cupressus lusitanica plantations on ridge sites. At present I am applying the method in the semiarid mountains of Tunisia to assess the effect of site preparation on soil moisture stress, and to evaluate relationships between soil moisture stress during the long summer drought and the regeneration of Pinus halepensis.2. The method may be applied to construct soil moisture retention curves, i.e., the relationship between moisture content and moisture stress, which is an important hydrological constant of a soil. Derivation of these curves, or certain points on them (usually chosen to correspond to field capacity or the permanent wilting point), is arrived at laboriously in the customary methods using tension tables and pressure plate apparatus - equipment, moreover, which is often not available in developing countries. Williams and Sedgley (1965) used a filter-paper method to estimate the 15-atmosphere percentage of soils, and Fawcett and Collis-George (1967) expanded that method to construct entire soil moisture retention curves. Del Valle and Cadavid (1970) who tested the variability of McQueen and Miller's method also constructed soil moisture retention curves for several profiles of soils derived from volcanic ash. I have outlined a practical working procedure for deriving these curves with the filter-paper method (Tschinkel, 1972a) and have applied the procedure to their data. The calculations can be made either with a desk calculator or with FORTRAN programmes and regression techniques for curve fitting. Recently Miller and McQueen (1972) derived relationships that can be used to estimate quantities of moisture in soils at different levels of moisture stress. An article by the same authors on approximating soil moisture retention curves from limited data is in press.
BRANSON, F.A., MILLER, R.F. & McQUEEN I.S. 1965, Plant communities and soil moisture relationships near Denver, Colorado. Ecology, 46(3):311-319.
BRANSON, F.A., MILLER, R.F. & McQUEEN I.S. 1970, Plant communities and associated soil and water factors on shale-derived soils in northeastern Montana. Ecology, 51(3):391-407.
FAWCETT, R.G. & COLLIS-GEORGE, N. 1967, A filter paper method for determining the moisture characteristics of soil. Aust. J. exp. Agric. Anim. Husb. 7:162-167.
GARDNER, R. 1937, A method of measuring the capillary tension of soil moisture over a wide moisture range. Soil Sci., 43:277-283.
HERRMANN, R. 1970, Vertically differentiated water balance in tropical high mountains, with special reference to the Sierra Nevada de Santa Marta/Colombia. International Association of Scientific Hydrology, Proceedings of the Reading Symposium, p. 262-273.
HERRMANN, R.1971, Die zeitliche Änderung der Wasserbindung im Boden unter verschiedenen Vegetationsformationen der Höhenstufen eines tropischen Hochgebirges (Sierra Nevada de Sta. Marta/Kolumbien). Erdkunde, Arch. wiss. Geogr., 15(2): 90-102.
McQUEEN I.S. & MILLER, R.F. 1966, Calibration and evaluation of a wide range method for measuring moisture stress in field soil samples. In. Water in the unsaturated zone. International Association of Scientific Hydrology, Proceedings of the Wageningen Symposium.
McQUEEN, I.S. & MILLER, R.F. 1968, Calibration and evaluation of a wide range gravimetric method for measuring moisture stress. Soil Sci., 106: 225-231.
McQUEEN, I.S. & MILLER, R.F. 1972, Soil moisture and energy relationships associated with riparian vegetation near San Carlos, Arizona. Washington, D.C., U.S. Geological Survey. Professional Paper 655-E. 51 p.
MILLER, R.F. 1969, Differences in soil chemistry induced by evaporation and flow of ground water. Washington, D.C., U.S. Geological Survey. Professional Paper 650-D, p. D255-D259.
MILLER, R.F. & McQUEEN, I.S. 1972, Approximating recurring moisture relationships in desert soils. In Eco-physiological foundations of ecosystem productivity in arid zones. International Symposium, p. 119- 122. Leningrad, "Nauka."
TSCHINKEL, H. 1972a, Factores limitantes del crecimiento de plantaciones de Cupressus lusitanica en Antioquia, Colombia. Revta Fac. nac. Agron., Medellín, 27(2):3-55.
TSCHINKEL, H. 1972b, Growth, site factors and nutritional status of Cupressus lusitanica plantations in the highlands of Colombia. Dissertation, University of Hamburg. 165 p.
DEL VALLE, J.I. & CADAVID, H. 1970, Retención, de humedad en andosoles de Antioquia determinada por el método del paper del filtro. Medellín, Universidad Nacional de Colombia, Facultad de Ciencias Agrícolas. 119 p. (Thesis)
WILLIAMS O.B. & SEDGLEY, R.H. 1965, A simplified filter paper method for determining the 15-atmosphere percentage of soils. Aust. J. exp. Agric. Anim. Husb., 5:201-202.
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