32 BULLETIN 1105, U. S. DEPARTMENT OE AGRICULTURE. 



RELATION TO YELLOW-PINE GROWTH. 



Soil favorable for germination and high percentage of survival. On account 

 of the thinness of the soil layer a comparatively low increment would be 

 expected. Roots can not develop downward as freely as on other types on 

 account of rock obstruction. 



Less density of grass cover than on other types, greater proportion of Muhlen- 

 bergia montava and Andropogon scoparius. Shrub Cewiothus more common 

 than on other divisions. 



Soil No. 9. 

 soil description. 



Brownish or reddish brown moderately friable loam to clay loam to 4 to 

 6 inches, becoming heavier in texture and more reddish with depth, thus 

 grading into very stiff, compact red clay. Bed rock is encountered at an 

 average depth of not more than 3 to 4 feet. This soil is found at bases of 

 slopes and in the drainage swales. The surface soil consists largely of colluvial 

 wash for at least 6 to 10 inches. Rather high percentage of rock fragments, 

 mostly of gravel size, scattered over the surface and incorporated in the soil. 

 Surface contains a little higher percentage of humus than divisions 24, 28, and 

 20. Does not bake or crust and is a little better aerated to a greater depth 

 than in the divisions just mentioned. Underlying clay difficultly penetrable; 

 highly retentive, once thoroughly wetted. 



RELATION TO YELLOW-PINE GROWTH. 



Percentage of seedling survival would be expected to be fair, but probably 

 somewhat less than the stonier soils. Increment should be nearly as good or 

 equal to that on soil 20. 



Fairly dense cover of the common grasses Festuca arizonica, Muhlenbergia 

 montana, and Blepharoncuron tricholepis. 



Soil No. 20. 



description of soil. 



Reddish-brown or chocolate-red compact clay loam grading into compact red- 

 dish clay which extends to 20 to 48 inches and thence rests either upon a thin 

 layer of stiff residual clay or upon the bedrock of basalt. The soil consists 

 mainly of the finer alluvial and pluvial wash deposited in the shallow swale 

 which traverses the plot from east to west. There may be a few scattered 

 stones and gravel on the surface or in the soil, but on the whole it is freer from 

 coarse rock fragments than other divisions. It is moderately impervious, but 

 highly retentive. Surface denuded of the natural veneer of grass mold bakes 

 and crusts slightly. 



RELATION TO YELLOW-PINE GROWTH. 



Natural reproduction may not be as abundant as on the more stony and 

 gravelly soils, but growth once started should be more rapid on the assumption 

 that there is greater fertility and total available moisture in the same volume 

 of soil. 



FesUwa arizonica-Muhlenbergia montana association forming a denser cover 

 than on other types. 





