2 BULLETIN 447, U. S. DEPARTMENT OF AGRICULTURE. 
irrigated during the following summer, the moist soil absorbed water 
much more readily than the dry soil. The dry soil required a longer 
flow of water to saturate it to a depth of 18 inches than did the soil 
containing more moisture. By irrigation, the water content of the 
moist soil was increased to a depth of 6 feet, while the dry soil showed 
no increase in water content below the second foot. Continuing the 
flow of water on the dry soil in order to get water into the lower 
depths was tried, but was discontinued for' the reason that the dry 
soil absorbed the water so slowly that a large amount of the flow was 
lost by run-off. 
The results obtained by Knorr on the sandy loam soils and those 
obtained from the experiments described in this paper on the gumbo 
soils are strikingly different. They bring out clearly the impracti- 
cability of trying to use the same methods on all soils. The character 
of the soil is an important factor in determining the degree of suc- 
cess of any method of water application. 
DESCRIPTION OF THE GUMBO SOIL OF THE BELLE FOURCHE 
RECLAMATION PROJECT. | 
The soil of the Belle Fourche Reclamation Project is a very heavy 
clay of the type classified by the Bureau of Soils as Pierre clay. 
The United States Bureau of Soils, in a reconnoissance soil survey of 
-western South Dakota, found that the soils of this type covered about 
seven and three-quarter million acres in South Dakota, or about 30 
per cent of the total area surveyed.? It is a residual soil, formed by 
the decomposition of shale, the partly decomposed shale being found 
at a depth of approximately 4 feet below the surface. This depth 
varies considerably with the location. 
Fine soil particles make up the greater portion of the soil. A 
mechanical analysis of the surface soil of this type shows that soil 
particles of the different sizes are present in the percentages shown 
in Table I. 
TasreE I.— Mechanical analysis of Pierre clay.% 
| 
Fine | Very fine : 
sand. sand. Silt. Clay. 
Medium 
sand. 
Coarse 
sand. 
Fine 
gravel. 
| ® 
| Per cent.| Per cent. len cent. | Per cenit. | | Per cent.| Per cent.| Per cent. - 
PeTCTEG Clave: sa BEG ne eee 0.2 1S a 1.4 | Seo 13.0 | 43.2 35.0 ie 
| zi | 4 
a Strahorn, A. T.,and Mann, C. W. Op. cit. 
Analyses of the subsoil are not available, but the textures of the 
second foot and third foot indicate that the percentage of clay at 
1 Strahorn, A. T., and Mann, C. W. Soil survey of the Belle Fourche area, South 
Dakota. U. S. Dept. Agr., Bur. Soils [Adv. sheets—Field Oper., 1907], 31 p., 1 fig., 
2 maps. 1908. 
2 Coffey, G. N., and others. Reconnoissance soil survey of western South Dakota. U.S. - 
Dept. Agr., Bur. Soils [Ady. sheets—Field Oper., 1909], 80 p., 2 fig., 7 pl., 1 map. 1911. 
