WATER OF SOIL IN ITS RELATION TO PLANTS 261 



Relation of Texture to the Wilting Point of Kubanka 



Wheat 



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 point 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 



