352 NATURE AND PROPERTIES OF SOILS 



esis may be considered as best explaining soil acidity, sci- 

 entific and practical men are agreed that the addition of cer- 

 tain compounds of calcium and magnesium tend to alleviate 

 the detrimental condition. Conversely, almost every one is 

 willing to admit that the most reasonable cause of its develop- 

 ment is the loss or inactivity of certain bases. A lack of cal- 

 cium seems especially prone to allow an increased hydrogen 

 ion concentration to develop and may at the same time en- 

 courage the activity of certain toxic bases or produce malnu- 

 trition. The tendency of all soils in a humid region is, there- 

 fore, towards acidity, their condition depending on the activ- 

 ity of certain factors which seem to produce such a condition. 

 The four important factors generally specified as encour- 

 aging acidity are: (1) leaching losses, (2) cropping losses, 

 (3) absorption phenomena within the soil, and (4) fertilizer 

 residues. 



The loss of nutrient bases from the soil has already been 

 emphasized (par. 163) and the importance of such removal is 

 evident from the standpoint of plant nutrition. Over a period 

 of ten years, the removal of nutrients from the Cornell lysi- 

 meter soils, ^ by drainage and rotation cropping together, 

 amounted to 3702, 1741, and 942 pounds to the acre, respec- 

 tively, for lime (CaO), potash (KoO), and magnesia (MgO). 

 The loss of such amounts of bases cannot but permit the rapid 

 development of soil acidity. No matter how well supplied 

 the soil may be with favorable bases, it will in time become 

 acid. 



Absorption, in its influence on soil acidity, produces its 

 effect by rendering certain bases inactive rather than by 

 removing them from the soil. When the activity of such bases 

 as calcium is reduced by absorptive influences, not only does 

 the hydrogen ion concentration of the soil solution tend to in- 

 crease, but the hydrolysis of compounds carrying aluminum 

 and similar bases seems to be encouraged. The acidity as de- 



* Unpublished data, Cornell Agr. Exp. Sta., Ithaca, N. Y. 



