SOIIv S6SSI0N. 



151 



enough of all except nitrogen for many large crops, could it all be 

 used. 



It is not sufficiently appreciated, although it should go without 

 saying, that a strong soil moisture solution, well charged with all the 

 essential plant food elements, making it a thoroughly balanced ration 

 for the crop growing upon the field, is indispensable to large yields. 

 Indeed, just as in the case of growing and producing animals, the body 

 must be kept charged with blood rich in all that is essential to increase, 

 so it must be with crops ; their sap must be loaded and to spare with 

 everything that makes for growth; aiifl just as a rich blood can only 

 be maintained out of a rich solution in the alimentary canal, ever re- 

 inforced by good air, so a strong plant sap can only be continuously 

 supplied to the crop when its roots are ever immersed in a soil solution 

 rich in all that is needed, and well aerated. The next table shows how 

 different was the plant sap in the crops growing on the good and on 

 the poor soils. 



Amount of plant food elements in the sap of plants, per equal areas, 

 growing on good and on poor s,oil : 



Phophoric 



Acid P. 



lbs. 



Sulphuric 



Acid S. 



lbs. 



Total 

 lbs. 



Good soil... 

 Poor soil 



11.8 

 4.6 



5.5 

 1.3 



205.1 

 61.1 



From this table it is seen that the same number of plants, growing 

 upon an equal area of good soil, were able to take up from the soil 

 through the soil moisture in the same time nearly three times as much 

 potash, as measured by the amount contained in the plant sap, over 5 

 times as much lime, 6 times as much magnesia, 7 times as much nitrogen, 

 more than double the amount of phosphoric acid, and 4 times the amount 

 of sulphuric acid. Associated with this stronger nutritive solution in 

 the soil, and with the sap of the plants richer in the elements which 

 contribute to growth, there was a yield nearly 2.5 times on the stronger 

 soil than that which developed on the poorer ^il. 



We have reason to think that, in the ultimate analysis, an exhausted 

 soil is one in which it has become impossible for natural processes to 

 maintain a sufficiently strong nutritive solution to meet the needs of 

 rapid growth. But with such large amounts of the essential plant food 

 elements present in the root zone of most agricultural soils ; and with 

 so much as we have shown to be present, even in the poorer soils, 

 which may be readily removed with water, it may appear strange, at 

 first thought, that reduced yields can result froiti a deficiency of plant 



