588 STATE BOARD OF AGRICULTURE. 



THE FREEZING POINT METHOD AND THE FERTILITY OF SOILS. 



It should be sd'ongly enipliasized that no claim is made that by means 

 of the freezing point method the fertility of the soil can be delermined. 

 Such a claim would be almost absurd since the freezing point method 

 indicates only concentration of solution and tells nothing of the chemi- 

 cal composition of this solution. A soil may possess a solution of high 

 concentration and yet this concentration may be composed entirely of 

 salts which do not contain the plant food elements. 



What is claimed is that the freezing point method furnishes: (1), in- 

 formation concerning the concentration of the soil solution from any 

 maximum moisture content to a very low water content. 



(2) It tends to compare approximately the salt content or concen- 

 tration of solution of soils and especiall}^ of the extreme types of soil, 

 at an equivalent moisture content. This equivalent moisture content, 

 however, is difficult to obtain as has been seen. 



(3) It detects readily the abnormal concentration of solution of un- 

 usual soils. Thus, Director Hartwell had two soils in the green house 

 which were heavily fertilized and were planted to carnations. The latter 

 failed to make any satisfactory growth. Director Hartwell sent us 

 samples of these soils to determine their lowering of the freezing point. 

 The test showed that the depression of these soils at a high moisture con- 

 tent or at the saturation point was about .600°C or about 30 times as 

 great as that of average soils. Unquestionably, therefore, the carna- 

 tions refused to make a satisfactory growth on account of this great 

 concentration of solution. Many similar experiences could be cited if 

 space permitted. 



(4) It shows the effect of application of fertilizers upon the con- 

 centration of the soil solution, as will be subsequently seen. 



(5) It reveals a most remarkable relation between the soil and the 

 water. 



(6) It can be employed to determine the wilting coefficient of soils. 



(7) It can be used to study the toxic effect of salt or the toxic effect 

 of alkali soils, upon plant growth, as the toxic effect is due not only to 

 the total soluble material "present but also to the total concentration 

 which is composed of total soluble material and ionization of this ma- 

 terial. 



All these facts are of the greatest importance in furthering our knowl 

 edge concerning the fundamental principles governing the soil solution 

 and undoubtedly that of the soil fertility. 



EFFECT OF APPLICATION OF SOLUBLE SALTS UPON THE CONCENTRATION OF THE 



SOIL SOLUTION IN THE SOIL. 



The effect of application of soluble salts upon the concentration of the 

 soil solution was also reinvestigated in the second study. The investiga- 

 tion, however, was greatly extended by employing a greater number of 

 salts and a larger number of soils. The soils numbered 67 as compared 

 with 10 in the first investigation, and varied both in origin and type. 

 They represented characteristic types of soil from 10 different states. In 

 fact they were the same soils which were used to determine the con- 

 centration of their solution at very low and high moisture content al- 

 readv considered. 



