338 STATE BOARD OF AGRICULTURE. 



the decomposition of neutral salts, hydrolizing salts or fixation of hydroxides 

 is not a distinguishing property of acid soils, and this being the case it is diffi- 

 cult to understand the basis of the present use of these chemical compounds, 

 except possibly soluble hydroxides under conditions of neutral equilibria, for 

 qualitative or quantitative determinations of soil acidity or for lime require- 

 ment determinations. In fact, the results of this investigation show that 

 the factors causing fixation from neutral salts and those concerned with soil 

 acidity are diametrically opposed. The case of treating soils with KC2H3O2 

 and Ca(C2H302)2 has already been discussed. The quantities of uncombined 

 CiHsOi-ions found in the soil extracts were not a measure of the quantities 

 of potassium or calcium fixed by the soils from these salts ; but in case of the 

 KC2H3O2 treatments the quantities of C2H302-ions found in the soil extracts 

 were an approximate measure of the differences between quantities of potas- 

 sium fixed and calcium magnesium found in the solutions. Applying the 

 same reasoning to the Ca(C2H302) 2 treatments the quantities of C2H302-ions 

 found in the soil extracts would be roughly proportional to the differences 

 between quantities of calcium fixed by the soils and magnesium occurring 

 in the solutions. Replacing a soil element with another element from a 

 salt gives no moans of measuring the magnitude of soil acidity. Another 

 important point in this connection is because of the complicity of the reac- 

 tions involved, the titration of soil extracts with either acids or alkalies 

 will be attended by difficulties unless the chemical composition of the extracts 

 is known. Apparently the reaction of a soil is determined l)y quantity 

 relationships, not the relationships existing between the water soluble soil 

 material or the solubihty products of soil components, but between the 

 quantities of the active masses of the components involved. In other words, 

 all soils may contain reserve alkalinity and reserve acidity and the soil reac- 

 tion may be the result of mass action between the active masses of these 

 components. The term active mass referring in this connection to all the 

 material which could be brought in a condition to react. A neutral soil then, 

 would represent a case where the active masses of reserve alkalinity and 

 reserve acidity were equivalent, and soils containing un-eciuivalent active 

 masses of these components would Ije either acid or alkaline as the case might 

 be. 



Practical Considerations 



The statement has been made that the magnitude of fixation in soils is 

 closely related to their agricultural value, the soils fixing the greatest quantity 

 of substances being the best for agricultural purposes. Since it has been 

 shown that fixation from chemical salts depends chiefly upon the calcium 

 and magnesium content of soils, it follows that the calcium and magnesium 

 content of soils is an important fertility factor. The quantity of calcium 

 and magnesium in itself, however, is probably not nearly as important from 

 the fertility standpoint as is the ratio between the quantity of active calcium 

 and magnesium and other soil materials, namely, acid silicates; because 

 alkaline soils as a class are usually more fertile than acid soils and alkaline 

 soils have greater ratios of calcium and magnesium to acid silicates than acid 

 soils. The agricultural value of a soil then probably depends to a certain 

 extent upon its active quantity ratio of calcium and magnesium to acid silcates. 



Liming increases fixation and thereby gives a soil a certain potential 

 value enabling it to better conserve its fertility, as represented by the fer- 

 tility products of soil processes or applied as fertilizers; to better prevent 



