igig] ALWAY, McDOLE, &• TRUMBULL—SUBSOIL 205 



Shantz (10) extend would not suffice to explain the dry condition 

 of the deeper subsoil which we encountered. 



The persistently moist condition of the deeper subsoil of the 

 humid prairies is to be attributed to the fewness of the roots 

 developed in them. When deep rooted perennial plants such 

 as alfalfa or forest trees are introduced, their subsoil moisture 

 is utilized to a much greater depth. It is evident that on these 

 a forest once established should be able to maintain itself if pro- 

 tected from fires. The subsoil moisture conditions in general 

 would indicate that the natural condition of grassland in eastern 

 Nebraska is due to other causes than soil moisture conditions, 

 while in western Nebraska it may be fully accounted for by those 

 alone. 



The distribution of carbonates in the first 6 ft. of soil in the 

 prairies at McCook and Wauneta indicates that in prehistoric times 

 the climate was similar to that now prevailing (4). Carbonates 

 are found in the surface foot or two only in almost negligible 

 quantities, while in the fourth, fifth, and sixth feet they constitute 

 from 3 to 6 per cent of the weight of the soil. 



Summary 



1. During a 6-year period, in which the weather was exception- 

 ally favorable for a study of the minimum moisture content of the 

 subsoil, moisture studies were carried out on Nebraska prairies, 

 both in the buffalo-grass formation in the southwestern part of that 

 state, where the climate is typically semi-arid, and in the prairie- 

 grass formation near Lincoln, which Hes within the limits. of the 

 humid region. The fields were sampled to a depth of 6 ft. or more, 

 and in the case of every sample the hygroscopic coefficient as well 

 as the moisture content was determined, and the moisture condition 

 is expressed as the ratio of moisture content to hygroscopic coeffi- 

 cient, this having the advantage of expressing the relative moistness 

 while at the same time indicating whether either free water (i . i or 

 above) or growth water (1.6 or above) is present, and if so the 

 amount of each. 



2. The subsoils of the semi-arid prairies were characterized by 

 their persistent dryness. Usually throughout more or less of the 



