256 AGRICULTURAL INDICATORS. 



gation and by such economic considerations as markets and transportation. 

 Moreover, the method of conserving water-content by means of summer 

 fallow enables dry-farming to be practiced in regions where otherwise irriga- 

 tion would be the only successful method. On the other hand, where annual 

 cropping is the rule, dry-farming methods pass imperceptibly into those of 

 ordinary farming with good tillage in semi-arid and subhumid regions. In 

 spite of this, there is a general correspondence between cUmax associations 

 and types of farming. The tall-grass prairies are typical of regions in which 

 humid farming prevails. The mixed prairies and short-grass plains denote 

 country in which dry-farming of the annual crop type is more or less success- 

 ful. The bunch-grass prairies and desert plains characterize regions of scan- 

 tier rainfall, for the most part of the winter type, and hence are chiefly to be 

 correlated with dry-farming by means of summer fallow. Subclimax sage- 

 brush has practically the same indicator value as the associated grasses. 

 When these are tall-grasses the indications are of dry-farming with annual 

 cropping, and when they are bunch-grasses they indicate summer fallow 

 methods. Climax sagebrush is also an indicator of the latter when the rain- 

 fall does not fall below 10 inches. Over the major portion of the central Great 

 Basin, sagebrush indicates a cUmate in which crop production is impossible 

 without irrigation. This is likewise true of practically the whole desert scrub 

 cUmax except for small areas at higher altitudes or near its eastern limit, 

 where it approaches or mixes with the grassland. The indications of chaparral 

 are variable. While they are largely non-agricultural, chaparral resembles 

 scrub generally in its indication of dry-farming or irrigation practices, as is 

 true also of woodland where soil and topography are favorable. Montane 

 forest usually receives enough rainfall to make humid farming possible, 

 though both dry-farming and irrigation are practiced in the lower yellow-pine 

 belt. Most of the montane zone hes above the Umit of profitable agriculture, 

 and the occasional fields of hardy cereals are restricted to the warmer valleys 

 and lower slopes (plates 61 and 62). 



Edaphic indicators of types of farming. These are more local and hence 

 less important than the chmatic indicators just discussed. They are primarily 

 related to soil and water-content, and consequently are of the greatest service 

 in regions with marked soil characteristics, such as sandhills, bad lands, saline 

 basins, or in river or lake valleys with relatively high water-content. The 

 same farm may have lowland and upland areas, or may show considerable 

 variations in soil with corresponding indications as to types of farming. This 

 is particularly true of the wet valleys in the sandhills of Nebraska and of the 

 many river valleys with a generally westward direction in Nebraska and 

 Kansas. The wet valleys are marked by meadow communities, and many 

 of them are susceptible of farming by the usual methods. The river valleys 

 are occupied by similar communities of which Andropogon, Agropyrum, Cala- 

 movilfa, Elymus, or Spartina are the dominants, or they may be characterized 

 by the presence of scrub. In either case the indications are for subhumid 

 farming, especially during the wet period of the climatic cycle. 



Shantz (1911:85) has pointed out the agricultural significance of the 

 difference between lighter and heavier soils in passing to the westward. The 

 lighter soils conserve water to a much larger degree, and hence require less 

 intensive methods of cultivation than do the heavier ones. In some regions, 



