WATER OF SOIL IN ITS EEL AT ION TO PLANTS 261 



Relation of Texture to the Wilting Point of Kubanka 



Wheat 



Soil 



Moisture 



EQtrIVALE^T 



Wilting Point of 

 Kubanka Wheat 



Sand 



Fine sand 



Fine sand 



Fine sand 



Sandy loam 



Sandy loam 



Sandy loam 



Loam 



Loam 



Clay loam 



Clay loam 



1.55 



4.66 



5.50 



6.74 



9.70 



14.50 



18.60 



23.80 



25.00 



27.40 



29.30 



.86 



2.60 



3.33 



3.70 



4.80 



9.60 



8.84 



12.40 



13.90 



14.50 



17.10 



Briggs and Shantz have attempted to express this 

 correlation by a formula which, while very inaccurate, 

 shows in general the relationships already expressed. 

 The correlation in this case is made between the wilting 

 point and the mechanical composition of the soil : — 



Wilting point = .01 sand + .12 silt + .57 clay (error 10 



per cent) 



183. Available and super-available water. — Advanc- 

 ing from the wilting, or critical, moisture content of a 

 soil, all the remaining capillary water is found to be avail- 

 able for normal plant use. However, when free water 

 begins to appear, a condition adverse to plant growth is 

 established, and as the saturation pomt is approached 

 this condition becomes more adverse. This free water 

 is designated as the super-available water, since it is 

 beyond the available and its presence generates condi- 

 tions unfavorable to plant growth. The upper limit of 



