PLANT SUCCESSION 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 chemical 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 striking difference is found in the total nitrogen 
/O 20 
Sep/: J 
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. — Chemical properties of soil supporting small wheat grass and soil sup- 
porting the ruderal- weed consociation. 
Soil. 
Lime 
(CaO). 
Potash 
(K-O). 
Phosphoric 
acid (P g O s ). 
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- 
