Emil Truog 39 



An examination of the analytical data for timothy reveals a much 

 different situation in this connection. This plant (on a milliequivalent 

 basis) requires more than double the amount of the acidic than of the 

 basic constituents. There may be some question as to the propriety of 

 including silica (Si0 2 ) and chlorine in these calculations because of the 

 weakness of the former as an acid and nonessentiality of both as plant 

 constituents. However, even when these two constituents are disre- 

 garded in the calculations, a considerably greater equivalent amount 

 of acidic than of basic constituents is still required by timothy. Thus, 

 the timothy plant can absorb a considerable portion of its nitrogen and 

 sulfur needs in the form of free nitric and sulfuric acids without up- 

 setting the internal nutrient balance of needed acids and bases. 



In the above considerations it is assumed that all the nitrogen derived 

 from the soil is absorbed as the nitrate. Absorption by plants of some 

 of the nitrogen in the ammonium form as a cation will not alter ma- 

 terially the deductions made, since alfalfa will still have a much greater 

 base requirement than timothy. 



It has been noted that alfalfa often grows much more satisfactorily 

 on distinctly acid soils if these soils happen to be well supplied with 

 available nitrogen. However, in the case of nonacid and very slightly 

 acid soils, the supply of available soil nitrogen is not crucial providing 

 the alfalfa is properly inoculated. The foregoing discussion accords with 

 these observations. When the alfalfa has access to soil nitrogen, much 

 of the nitrogen absorbed carries a base with it even though the soil is 

 acid. However, if the plant is dependent upon atmospheric nitrogen, 

 then no bases are carried in with the nitrogen, and the plant must 

 compensate for this by absorbing from the soil considerable amounts 

 of the required bases in the form of the carbonate or bicarbonate, such 

 as calcium bicarbonate. The carbonates and bicarbonates, because of the 

 weakness of the acid radical, function in the plant much like a free 

 base. Only when soils are not very acid can they be obtained in ade- 

 quate amounts for plants like alfalfa which have a high requirement. 



The indirect influence 



The indirect influence of soil reaction on plant growth may be 

 exerted in a number of ways. Of tremendous importance is the inflq- 



