162 



"(2) That tliis acidity can be removed by exposure of the soil either to water 

 and air tosietlicr (as when it is repeatedly washed with water) or. to some 

 extent, by exposnre to air alone (as when it is spread out in the open in the 

 dry condition) : after this it will grow quite good crops of barley and wheat. 



"(3) That the failure of crop growing does not consist alone in the removal of 

 lime from the soil, inasnnich as if the acid be removed (as above) the soil still 

 has enough lime to support a healthy ci'op. 



" (4) That the oat crop is not injiu-iously affected by the soil acidity of the 

 extent that wheat and barley are. 



"(.J) That removal of lime from a soil takes place far more rapidly when 

 annnonia salts are used than when nitrate of soda is applied, and that muriate 

 of annnonia is a more i)()tent agent in removing lime than sulphate of annnonia, 

 the latter, however, being more exhaustive of lime than nitrate of soda. 



"(0) That the effects of the acidity thus produced can not be removed by 

 the use of a neutral salt like calcium chlorid, but that this can be done by the 

 emjiloyment of lime, after which healthy crops of barley and wheat can be 

 again secured. 



"(~) That the acidity would seem to be due not to soluble mineral acids, but, 

 possibly, to weak organic acids or to acid salts." « 



THEORIES AS TO THE CAUSE OF .SOIL ACIDITY. 



Samples of the Ohio soil have been examined by the Bureau of Soils, U. S. 

 Department of Agriculture, and Doctor Whitney. Chief of the Bureau, reports 

 as follows : 



" The soil grains themselves are very acid to litmus and a faintly alkaline 

 solution of phenolphthalein, but not to methyl orange. The acpieous solution 

 prepared from the soil is only slightly acid as compared with the acidity of 

 the soil grains themselves, showing that the acid of the soil is only very 

 slightly removed from the soil grains by water. This slight acidity is more 

 marked with phenolphthalein than with litnuis. but this is wholly due to the 

 greater sensitiveness of the former indicator. Litmus paper contains always 

 a trace of alkali, and is, therefore, not sensitive to such small amounts of acid. 

 When a carefully prepared litmus solution is used as an indicator with a 

 sufficiently large amount of soil extract the acid reaction is readily and definitely 

 noticed. This acidity persists even after boiling for a considerable time, in 

 fact, after concentrating the solution to one-tenth of its original volume, thus 

 showing that the acid reaction is not due to carbonic acid. As. however, the 

 solution, either in its diluted or concentrated form, does not show an acid 

 reaction with methyl orange, it follows that the acid present belongs to a 

 class of weak acids, probably an organic acid, or i)ossibly an acid phosphate. 



" On heating the soil to redness for a sufficient length of time to burn out 

 the organic matter and then treating with water containing litnuis or phenolph- 

 thalein the soil does not show an acid reaction, but evidently an alkiline one, 

 indicating that the acidity in its original condition was due to an organic acid 

 and not to an acid phosphate. 



*' The following considerations will show that this acid substance in itself 

 is not deleterious to the wheat plant, and that the beneficial effect of lime on 

 this soil is due to some other cause than the neutralization of the acid. 



" In the first place, we find that when the soil is made faintly alkaline 

 with sodiinn carbonate or with sodium liydr;ite the transiiiration and growth 

 of the i)lant is not increased nearly ;is much as upon the application of lime. 

 Furthermore, by the addition of 2.")0 i)arts per million of concentrated sulphuric 

 or hydrochloric acid to these acid soils there is no apparent effect seen in the 

 iransi)iration or in the green weight of the crop. Even stronger arguments 

 follow. 



"The addition of 1<I0 parts per million of nitrate of soda to the Wooster 

 soil increases the transi»iration from the ])lants and the green weight of the 

 plant fully as much, if not more, than l.OdO parts i)er million of lime: that is 

 to say, tlie nitrate of soda in the altove proportion appears to be quite as 

 efficient as the lime in increasing ]il:int growth. The soil, after treatment 

 with the nitrate of soda, in which the jilant growth is fully as satisfactory 

 as when the lime is used, is still acid, even after the i)lants have grown in the 

 soil in this satisfactory maimer for some time. In other words, the nitrate of 

 soda does not correct the acidity of the soil * * * y^t does increase the 

 plant development without removing or changing the acid condition. 



p Jour. Roy. Agr. Soc. England, VA (1903), p. 301, 



