2 BULLETIN 447^ V. S. DEPARTMENT OF AGRICULTURE. 



irrigated during the following summer, the moist soil absorbed water 

 much more readily than the drj 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 trjdng 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 approximatelj^ 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. 



Table I. — Mechanical analysis of Pierre claij." 



Soil. 



Fine 

 gravel. 



Coarse 

 sand. 



Medium 

 sand. 



Fire 

 sand. 



Very fine 

 sand. 



Silt. 



Clay. 





Percent. 

 0.2 



Per cent. 

 1.1 



Percent. 

 1.4 



Per cent. 

 5.5 



Per cent. 

 1.3.0 



Per cent. 

 43.2 



Percent. 

 35.0 











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.. 



- Coffey, G. N., and others. Reconnoissance soil survey of western South Dakota. U. S. 

 Dept. Agr., Bur. Soils [Adv. sheets — Field Oper., 1909], 80 p., 2 fig., 7 pi., 1 map. 1911. 



