EXPERIMENT STATION BULLETINS. 817 



THE FREEZING POINT METHOD AS A NEW MEANS OF DE- 

 TERMINING THE NATURE OF ACIDITY AND 

 LIME REQUIREMENTS OF SOILS. 



Technical Bulletin No. 27. 



INTRODUCTION. 



Perhaps no other single subject in soils is receiving at present more 

 attention and investigation than that of soil acidity. Again, probably 

 no other soil problem is so rich in laboratory methods^ as the acidity of 

 soils. Both of these facts unmistakably go to indicate that the subject 

 per se is of urgent importance and that probably none of the present 

 methods is proving entirely satisfactory for its solution. 



That the subjct is of great and urgent practical importance can scarcely 

 be questioned. It appears now to be an established fact that the so- 

 called acidity of soils is proving to be a limiting factor in crop growth, 

 at least for many agricultural plants, and that the infertility of many 

 soils, in part or in whole, may be safely attributed directly or indirectly, 

 to this factor. The necessity, therefore, of correcting this acid condition 

 of soils and thereby rendering them more efficient and productive, is of 

 paramount importance. 



Experience has shown that when the acid soils are treated with lime in 

 its various forms the growth of some crops is greatly increased, while 

 that of others, very little if any. This has led to the logical conclusion 

 that the acid condition of soils affects the varions plants differently. 



Since this is true, then it would appear that probably no soil acidity 

 laboratory method could ever be expected to tell exactly to what extent 

 the soil acidity should be corrected by the application of lime. This 

 point would have to be settled by field experiments. 



Most that a soil acidity laboratory method might ever be expected to 

 do from the practical standpoint, is to show the maximum lime require- 

 ment of soils and then apply the lime according to the crops planted. 

 Any soil acidity laboratory method, therefore, that would be able to indi- 

 cate definitely and correctly the maximum lime requirement of soils, 

 would be of the greatest value. 



It appears very doubtful if any of the present soil acidity methods 

 gives the true lime requirement of soils. Thus, take the Veitch method 

 which is quite generally considered to be probably the most satisfactory 

 from the practical standpoint, i. e., it comes closer in indicating the true 

 lime requirement of soils than any other method, although many of the 

 other methods show almost identical results. A critical consideration 

 of the nature of the soil mass and the kind of indicator employed seems 

 to point very strongly to the fact that this method probably does not 

 indicate the tottil maximum lime requirement of soils. A consideration 

 of the soil mass shows that it is composed mainly of silicates of the 



(1) It is not deemed necessary to review the numerous soil acidity methods that have been pro- 

 posed, since several of the recent articles on soil acidity contain quite complete reviews of these different 

 methods Perhaps the most complete resume of all the various soil acidity methods is contained in 

 a recent bulletin written by Dr. W. Frear entitled: Sour soils and Liming. Bulletin 261, Dept. of Agr., 

 Commonwealth of Pennsylvania. 

 103 



