EXPERIMENT STATION BULLETINS. 527 



In Table VIII it will be noted in Soil 34 that the nitrogen as ammonia 

 remains the same with one or two exceptions, but in Soil 35 there is a 

 decrease. In all cases the nitrogen as nitrite increased while the nitrate 

 decreased, with the exception of 35 II where it increased. The change in 

 this case was between ammoniacal nitrogen and nitrate nitrogen. In 

 nearly all cases there was a very slight decrease in the total nitrogen 

 (snm of the different forms of nitrogen) in the successive i)ortions of 

 soil solution. 



Biological. 



Onl,y a very small percentage of the bacteria are removed from the 

 soil since the soil in the cylinder acts as a filter in holding back most of 

 the suspended substances. The soil acts on the same principle as a filter 

 bed in a water purification plant. If the cylinders are allowed to stand 

 too long a very marked anaerobic decomposition takes place which is 

 quite marked in clay soils or those with considerable organic matter as 

 evidenced by the disagreeable odor given oft'. In Table VIII there will 

 be noted a slight <lenitrification, — less nitrates and more nitrites. This 

 is especially true in 34 I and II, and 35 I. 



This soil solution is now being used in connection "with the study of 

 the microbial decomposition of nitrogenous compounds in the soil. 

 Favorable progress has been made. Mr. O. M. Gnizit, in this laboratory, 

 has used the soil solution to studj^ the effect of some acids, alkalis and 

 inorganic salts upon soil bacteria and has found some interesting re- 

 sults. A report on the results of these investigations is now being 

 prepared for publication. 



SUMMARY. 



Soil solution is a hoinogeneous mixture of water (solvent) and the 

 soluble ingredients of the soil (solutes.) 



The water itself does not bring into solution all the solutes it contains 

 without the aid of some of the substances that have been already dis- 

 solved. 



The study of the soil solution is of a great importance because this 

 solution plays an important role in soil changes or transformations, and 

 because it furnishes a medium for plant and microbial growth. 



Drainage waters contain too much of some ingredients and too little 

 of others to give any definite information as to the soil requirements. 



Soil extracts contain more of some ingredients, and also other ingre- 

 dients, than are generally present in the natural soil solution readily 

 available for the plant. This is due to the action of the acids, water, 

 etc., used in making the extracts. 



The artificial root is applicable to those soils of high moisture con- 

 tent and furnishes only a small amount of solution. 



The centrifuge does not furnish sufficient amount of solution for any 

 extensive study. 



Schloesing's and also Gola's method are not applicable to soils having 

 a low moisture content, while Istcherikov's method can be applied to 

 soils of low moisture content, but is objectionable because alcohol has a 

 solvent action on some of the soil i^articles. 



