SOILS FERTILIZERS. 427 



stance; effect of absorption npon the physical condition of the soil; and perco- 

 lation, inc'Inding reclamation of blaclv alkali soil by leaching, efficiency of 

 calcium sulphate in removing black alkali, and absorption of potassium from 

 carbon:ite solution. 



" The principal object of this work has been to determine how absorption 

 controls the concentration of the soil solution, which is the great nutrient 

 medium upon which plants feed, and, further, to determine the effect of ab- 

 sorption upon the structure of the solid portion of the soil in modifying its 

 power to hold and maintain the soil solution for the continued use of the plant. 

 As a result of this work it has been shown that a number of modifying factors 

 enter into each particular case, which makes it impracticable to fornuilate a 

 simple general law which will account quantitatively for the distribution of a 

 dissolved substance between the liquid solution and the absorbing medium, 

 although it is brought out very clearly that under the ideal conditions, where 

 there is no change in the surface of the absorbing medium, a simple mathe- 

 matical law can be predicated a priori, which law is approximately realized 

 in practice in those cases where it is known that the least amount of change 

 takes place in the absorbing surface. . . . 



" In the experiments described the materials used are not always fertilizer 

 salts or constituents of the soil itself, since other substances, particularly cer- 

 tain dyestuffs, are better adapted to obtaining a more detailed knowledge of the 

 mechanism of absorption. In general, it may now be stated that where dis- 

 turbing influences are not great the mathematical formulation may be made 

 both of the time rate and of the absorption and distribution of the material 

 between the solid and the liquid. The disturbing influences, however, are 

 quite important in most cases actually met in practice, and therefore a de- 

 tailed study of some of them v^-as undertaken. The most imi)ortant of these is 

 the change in the physical character of the soil itself, consequent upon the 

 absorption of the dissolved materials. In some cases, notably with acids and 

 with lime, the soils assume a ' flocculated ' structure, i. e., a great many of the 

 ultimate grains form larger aggregates or ' ball together ; ' and in other cases, 

 especially with alkalis, the soils are deflocculated, each grain standing out 

 separate and distinct from the others. This change in the structure of the soil 

 is of the utmost importance in influencing the physical condition of the soil, 

 which in turn influences the drainage condition, the aeration of the soil, its 

 capacity to hold the soil solution and control its movement through the soil, 

 the composition of the soil solution, the character and rate of the chemical 

 changes taking place in the soil solution ; and, in fact, in influencing directly 

 both the physical and chemical factors which are the most important in 

 governing the proper growth of plants." 



The results of experiments with alkali soils from Yakima, Wash., and Fresno, 

 Cal., indicate that " neutral salts, such as chlorids, in the presence of carbon- 

 ates are comparatively easy to leach from the soil. With continued leaching 

 of the soils containing ' black alkali ' there is an increase in the rate at which 

 percolation takes place, due probably to the reduction of the amount of alkali 

 present and to a consequent effect on the physical structure of the soil. With 

 continued leaching there is a comparatively rapid reduction of normal carbon- 

 ates in the soil water, due in large measure to conversion to bicarbonates, 

 Bicarbonates are rapidly removed at first and then continue to be slowly re- 

 moved in the soil water in very small quantities, diminishing for an indefi- 

 nite period. The leaching curves conform fairly well to the rate equation, 

 dy 

 ^=/i {A—y), proposed by Schreiner and Failyer. Soils containing 'black 



alkali' can be reclaimed by leaching (i. e., flooding with underdrainage), but 



