724 EXPERIMENT STATION RECORD. 



Studies on the relation of the nonavailable water of the soil to the hy^o- 

 scopic coefficient, F. J. Ax way (Nebraska Si a. Research Bui. 3, pp. 5-122, 

 figs. 37). — In the studies reported " water-tight cylinders, 6 ft. long and holding 

 about 100 lbs. of soil, were either filled with dry soil, saturated with water and 

 drained before seaiing at the bottom, or filled with soil already containing the 

 desired amount of moisture. These were removed to a greenhouse, seeds of 

 wheat, milo maize, beans, or maize planted in the moist surface soil and no more 

 water added, the resulting plants being allowed to grow until they matured 

 normally or died. Upon the death of all the plants in a cylinder it was opened, 

 both the total and the free water in each 3-in. section of soil determined, and 

 the distribution of roots observed. In other cylinders three perennial desert 

 legumes were grown until they died or were near their limit of endurance, 

 then the cylinders were opened and the moisture content and root distribution 

 determined. 



" In all the cylinders bearing plants, a hard crust developed below the surface 

 mulch of dry soil, but it seemed to have no injurious effect. The formation of 

 such a crust is to be regarded as unavoidable where during a prolonged period 

 of rainless weather plants with a well developed root system and a very limited 

 amount of moisture in the subsoil are transpiring a large amount of water. 



" In their ability to exhaust the moisture of the subsoil before dying. Red 

 Fife wheat, Kubanka wheat, milo maize, Mexican beans, and maize showed lit- 

 tle difference, but in their ability to continue alive after first showing serious 

 injury from drought they exhibited marked differences. The interval between 

 waiting and death in the case of the beans amounted to only a few days, but in 

 that of wheat and milo maize it often extended to many weeks. Where there 

 was a well developed root system and no remarkably unfavorable conditions 

 occurred before the death of the plants, the moisture content could be reduced 

 by any of these plants almost to the hygroscopic coefficient. 



" In experiments with perennial desert legumes the plants remained alive 

 after the water content had fallen slightly, but distinctly, below the hygroscopic 

 coefficient, even to the point at which all the above mentioned annual crop 

 plants had died. Under favorable conditions these legumes adjusted themselves 

 to the gradually increasing dryness of the soil by dropping their leaves one by 

 one; but where, with the subsoil moisture already reduced to near the hygro- 

 scopic coefficient, conditions causing an abnonnally high transpiration sud- 

 denly set in, death occurred without the leaves having dropped. While the 

 experiments furnish no evidence of any ability on the part of these legumes to 

 utilize for growth the last portion of free water, they indicate that this ix>r- 

 tion has a very high value for the maintenance of life and that even some of 

 the water below the hygroscopic coefficient may be available for the maintenance 

 of life in these plants. 



" In the portions of a semiarid subsoil where roots are well developed the 

 final content of free water is independent of the distance from the surface, 

 except where the stored water is much in excess of the amount required for 

 the complete maturity of the plant. 



" When the portion of the subsoil in immediate contact with the roots con- 

 tains only a comparatively small amount of free water, crop plants may die 

 quickly if conditions are such as to cause an unusually rapid transpiration. 

 An abundance of free water in deeper portions of the subsoil, in which but few 

 roots have been developed, may not avail to carry the plaut over such a critical 

 period. 



" The economy in the u.se of a certain amount of free water stored in the 

 subsoil may be much affected by its distribution. A high content confinetl to 

 the portion of the soD near the surface may induce a rapid growth of the 



