424 Mineral Nutrition of Plants 



from the soil but not the amount. It is certain that liquid water may not 

 move through a soil without carrying solutes with it. A vast amount 

 of data on leaching has been provided by lysimeter studies. Kohnke 

 et al. (7/) have provided an excellent bibliography and summary of 

 the information available. Since soils have virtually no adsorptive 

 capacity for nitrate and chloride ions, these two anions are readily 

 leachable and the quantities of these ions lost by leaching are rather 

 closely related to the quantities present in the soil and the amount of 

 percolate. The sulfate and bicarbonate ions are also readily leachable, 

 whereas phosphate is usually present in leachate in very small quanti- 

 ties, if at all. 



Loss of nutrient cations by leaching will be conditioned by base ex- 

 change phenomena. Of the exchangeable bases usually found in soils, 

 sodium has a relatively low energy of retention by adsorption surfaces 

 and is most readily leachable. Consequently, it has been readily leached 

 from humid soils, and therefore it is not prevalent in percolate from 

 soils of humid regions in marked contrast to that from soils in arid 

 regions. Potassium also has a relatively low energy of retention by soil 

 colloids, but it may readily become fixed within the crystal lattice of 

 soil clays. Consequently, it usually occurs in the leachate in rather 

 minor quantities. Thus, calcium and magnesium are almost invariably 

 the predominant cations in the leachate from lysimeters. As Kohnke 

 et al. (7/) point out, the actual quantity and quality of nutrient loss 

 by leaching depends on many different factors. Thus, coarse-textured 

 soils permit a greater proportional loss of nutrients than fine-textured 

 soils, and a porous-crumb structure favors greater percolation than a 

 single-grain structure. The type of soil cover may markedly affect nu- 

 trient loss by leaching. Thus, Lyon and Bizzell (yg) found that an 

 uncropped Dunkirk silty clay loam lost 28 times as much nitrogen by 

 leaching as compared to the same soil continuously cropped to grass. 

 There is much evidence to the effect that a vegetative cover lowers nu- 

 trient loss from leaching, by effecting a reduction both in the amount 

 of leachate and in the content of nutrients in the leachate. 



Dreibelbis (38) reported that drainage from elaborately designed 

 monolith lysimeters containing a Keene silt loam showed an average 

 annual loss of nutrients in pounds per acre as follows: calcium, 19.9; 



