42 
Pehr Olsson-Sefter. 
The surface cultivation which obtains in the so-called “ dry¬ 
farming ” process results in a loose open texture of the soil for two 
to four inches, which very materially influences the capillary 
movements of the soil-moisture. 
A similar result is noticeable in sand-formations where the sand 
is shifting. 
Further, the third point to be observed is the surface tension 
of the water. Whitney has discussed this in several bulletins 1 , and 
King 3 has experimentally proved many important questions in this 
connection. 
The general principles under which this factor acts may be 
summed up as follows:— 
1. Surface tension moves the water in any direction according 
to circumstances. 
2. When water is removed from the soil by evaporation or 
by plants, surface tension attracts more water to the spot. 
3. When rain falls on a dry soil, surface tension, together with 
gravitation, draws the water downward, even when gravitation 
alone would not be sufficient for that purpose. 
4. Surface tension of water is increased by salts, while it is 
lowered by organic matters. 
5. As the soil becomes drier the surface tension of the soil 
moisture is reduced. 
6. Surface tension of soil moisture is much lower than that 
of pure water. 
7. A soaking rain therefore increases the surface tension of 
the soil-moisture in the upper layers of the soil, and water is con¬ 
sequently drawn up from below. If excessive evaporation takes 
place immediately after the rain, not only the precipitated but also 
some of the water drawn from below may evaporate, and the soil 
is consequently left drier than it was before the rain. 
It is known that the capillary movement of moisture is greater 
in moist sand than in dry, as has been demonstrated by many 
experimenters, and that it takes place much more rapidly and rises 
to a greater height than the capillary rise of moisture in dry sand. 
But the combined action of the three factors mentioned and the 
1 Some physical properties of soils in their relation to moisture. 
U.S. Dept. Agr., Div. Soils, Bull. 4, 1892. 
Milton Whitney and Ralph S. Hosmer; Soil moisture. U.S. 
Dept. Agr., Div. Soils, Bull. 9, 1897. 
2 Observations and experiments on the fluctuations in the level 
and rate of movement of ground-water. U.S. Dept. Agr., 
Weath. Bur., Bull. 5, 1892. 
