LAND CLASSIFICATION. 243 



"The chief plant associations of eastern Colorado which indicate land of 

 agricultural value are the grama-bufifalo-grass association and the wire-grass 

 association (both of which belong to the short-grass formation) and the bunch- 

 grass association and the sand-hills mixed association (both of which belong 

 to the prairie-grass formation). 



"The chief vegetation types of eastern Colorado which indicate nonagri- 

 cultural land are the lichen formation, the Gutierrezia-Artemisia association 

 of the short-grass formation, and the blow-out association of the prairie- 

 grass formation. 



"Of the associations indicating land of agricultural value in eastern Colo- 

 rado, the grama-buffalo-grass association is most extensive, occupying the 

 greater part of the hard land. The bunch-grass and the sand-hills mixed 

 associations occur only in the sand-hill regions, while the wire^rass association 

 occurs on land of intermediate character. 



"In eastern Colorado the rainfall records show that the average monthly 

 rainfall is greatest during the period April to August. The increased heat in 

 July and August makes it almost certain that drought will occur in these 

 months. September and the later fall months have normally very Uttle 

 rainfall, and fall-sown grain often fails to germinate unless planted on land 

 in which water from rains earUer in the season has been conserved by summer 

 tillage. 



"Measurements show that from grama-buffalo-grass land a great amount 

 of water runs off and does not enter the soil. 



"Soil-moisture determinations in this type of land show that even during 

 periods of more than normal rainfall available soil moisture is limited to a few 

 inches of the surface soil. 



"On this account the vegetation is composed largely of short grasses which 

 have a great number of roots limited to the surface foot or two of the soil. 



"Moisture, even in the surface few inches of the soil, is often lacking ex- 

 cept during a few weeks in spring and early summer. The short grasses have 

 a comparatively short growing season. 



" Deep-rooted species are shut out by the lack of soil moisture in the deeper 

 layers of the soil and later-season plants are excluded because available 

 moisture is usually lacking, even in the surface layers, during late summer 

 and autumn. 



"An open cover of the short grasses indicates conditions less favorable for 

 crop production than a close cover. 



"The presence of deeper-rooted plants mingled with the short-grass vegeta- 

 tion indicates better conditions for crop production than those found where 

 the cover is purely of the short grasses. 



"The occurrence among the short grasses of plants characteristic of the 

 associations which indicate land without agricultural value suggests a less 

 favorable condition for crop production than where short grasses only are 

 found. 



"The presence of the wire-grass association indicates that there is a con- 

 siderable amount of water in the deeper layers of the soil, owing to the lesser 

 run-off and to the fact that the lighter soil permits deeper penetration. 



"Conditions indicated by the wire-grass association are favorable for both 

 shallow-rooted and deep-rooted plants and for a considerably longer period 

 of growth than those indicated by the grama-buffalo-grass association. 



"The bunch-grass association indicates a soil that is moist to a considerable 

 depth. Here conditions are more favorable for deep-rooted and late-season 

 plants than in land characterized by either the short-grass or the wire-grass 

 vegetation. 



