PLANT SUCCESSIOlsr AND RANGE MANAGEMENT. 



49 



small wheat-grass cover, but also to the comparatively high propor- 

 tion of humus, and hence water-holding power, of the wheat-grass 

 soil. 



Data showing the more important chemical constituents and humus 

 content of representative soils supporting short wheat grass and of 

 soil supporting ruderal weeds are given in Table 6. Except in the 

 amount of potash, the percentage of the chemxical constituents im- 

 portant as plant food is higher in the soils representing the small 

 wheat-grass lands than in the soils characteristic of the ruderal-weed 

 cover. The most strilring difference is found in the total nitrogen 



20 



Fig. 20. — Available and nonavailable soil moisture on an overgrazed area supporting a 

 sparse stand of ruderal vegetation, 1915. 



content. Also there is a wide difference in the humus content as de- 

 termined by incineration. 



Table 6. — CJieniical properties of soil supporting small ichent grass and soil sup- 

 porting the ruderal-iveed consociation. 



Soil. 



Lime 

 (CaO). 



Potash 

 (K^O). 



Phosphoric 

 acidCP205). 



Total 

 nitrogen. 



Loss by- 

 ignition 

 (humus). 



Small wheat grass 



Per cent. 

 1.49 

 1.26 



Per cent. 

 1.30 

 1.53 



Per cent. 



0.38 



.22 



Per cent. 



0.488 



.158 



Per cent. 

 14.65 



Ruderal weed 



6.64 













112655°— Bull. 791—19- 



