68 



manganese, the corresponding salts of the added bases 

 probably serving as an antidote to the salts of manga- 

 nese remaining in solution. According to this view,, 

 non-productive acid soils may owe their infertility to 

 the presence in the soil solution of salts of certain bases 

 which are injurious to plant growth, rather than to the 

 actual acidity of the soil. Support for this view may 

 be found from the fact that corn, cotton, cow peas, vel- 

 vet beans, soy beans, peanuts, and sorghum have been 

 grown on a set of plots on the Alabama Experiment 

 Station Farm, the soil of which has nearly twice as 

 high a lime requirement as have the plots from which 

 most of our soil extracts were obtained for the work 

 here given. The more acid soil receives moderate fer- 

 tilization and is productive, while the less acid plots 

 are heavily fertilized with nitrogenous fertilizers, and 

 are rapidly becoming non-productive. In other words, 

 productivity seems to be more dependent upon the na- 

 ture of the salts in the soil solution, than on the actual 

 acidity of the soil, (a) In this connection, it would be 

 ver}^ interesting to know the solubility of the manga- 

 nese in the soil solution of the variously treated plots of 

 the rotation experiment at the Pennsylvania Station. 

 For the soil on these plots. White has attempted to set 

 an acidity limit beyond which clover fails. Is 

 it actual acidity, or is it soluble manganese that 

 prevents the growth of clover, after the lime require- 



(a) Since the completion of this manuscript, a paper by B. 

 L. Hartwell and F. R. Peniber (Jour. Am. Soc. Agr., v. 10, No. 

 1) has come to liand in whicli a very similar view has been ad- 

 vanced, based on studies on soluble aluminum in acid soils of 

 Rhode Island. These writers state that "A moist acid soil upon 

 which most kinds of plants were unable to exist was kept in- 

 timately mixed for about two weeks with acid phosphate added 

 at the extraordinary rate of 28 tons per acre, after which let- 

 tuce was planted. This crop could not exist on the unphos- 

 phated soil supplied only with nutrients, but the soil treated 

 with acid phosphate produced a maximum crop, even more 

 than when lime replaced the phosphate. It was shown that 

 for a considerable time at least, the large amount of acid phos- 

 phate greatly increased the acidity, and yet a crop which 

 usually responds markedly to liming had made its maximum 

 growth on a very acid soil without the addition of any lime. 

 The solubility of the aluminum in dilute acetic and carbonic 

 acids had been markedly reduced by the phosphate, just as it 

 doubtless would be by lime or by a mixture of the two." 



"Determinations of the amount of what may be called active 

 aluminum may prove to be as desirable as acidity determina- 

 tions, and the lime requirement of a soil may be due to the 

 need for lime to precipitate toxic aluminum quite as much as 

 to neutralize acidity." 



