STATIONS WHERE WORK IS NOW IN PROGRESS. 11 



is on land lying above this projected canal that the drought-resistant 

 breeding is carried on. On part of the land (about 40 acres) the 

 native sod was broken in June, 1907, and this part has been kept 

 under thorough cultivation since that time. Another field of 20 

 acres was broken in 1908 and a third, of 10 acres, in 1909. 



The soil conditions here are different from those existing in the 

 greater part of the Great Plains region, the Belief ourche soil being a 

 heavy clay of the Pierre shale formation locally known as "gumbo." 

 This formation underlies nearly the entire State of South Dakota, but 

 it is covered by other formations except in the west-central part of 

 the State. There it constitutes the surface soil of practically the 

 entire area between the Missouri River and the Black Hills. It 

 forms a broad semicircle east of the Black Hills, in South Dakota, and 

 extends northward into Montana and southward into Nebraska. 

 The area covered in South Dakota is probably about 16,000 square 

 miles, being more than one-fifth of the area of the State. This soil 

 takes up water very slowly, so that during very heavy or long- 

 continued rains there is considerable run-off. It has, however, a 

 high capacity for absorbing water. Its moisture equivalent a is 

 about 29 per cent. The soil is therefore capable of holding a large 

 quantity of water and retains this moisture well when the surface is 

 so cultivated as to form a protecting mulch. If the surface is not 

 cultivated and is allowed to become dry and baked, the soil cracks 

 badly, owing to the considerable shrinkage in drying. These cracks 

 extend down 4 or 5 feet, allowing the subsoil to dry out. This is 

 often the condition of the fields during the winter and is probably 

 one of the factors which makes winterkilling of alfalfa common in 

 this region. The fine roots of the plants are evidently torn severely 

 in the shrinking of the soil. The large cracks about the plant pro- 

 mote drying of the roots and permit extensive and severe freezing. 

 It is the opinion of the writer that this extreme winter drought in the 

 alfalfa fields has as much to do with the killing of alfalfa plants as 

 the mere fact of low temperature. 



The average annual precipitation at the station probably does not 

 exceed 15 inches. At Ashcroft, S. Dak., which is about 65 miles 

 northwest of the Belief ourche Experiment Farm, the average annual 

 precipitation during the seventeen-year period from 1892 to 1909 

 was 14.2 inches. The average seasonal precipitation, April to August, 

 inclusive, was slightly over 9 inches. At the Bellefourche station 

 records of the seasonal (April to August) rainfall have been kept for 

 only two }^ears. The totals are as follows: 1908, 8.6 inches; 1909, 



a As defined by Briggs and McLane in Bulletin 45, Bureau of Soils, U. S. Depart- 

 ment of Agriculture, this term indicates the percentage of moisture to dry weight of 

 soil that remains after a centrifugal force equivalent to 1,000 times gravity has been 

 applied to the saturated soil. 

 196 



