CHAPTER VII 

 MINERAL NUTRIENTS 



IN a physiological sense the common fertilizers, or "arti- 

 ficial " fertilizers, sold upon the markets of a large part 

 of the world are, with respect to plants, soil nutrients or 

 amendments. A study of fertilizers and of conditions and 

 factors governing the use of these under diverse field con- 

 ditions constitutes a special phase of agronomic or soils 

 work. At all points this field of work overlaps physiolog- 

 ical inquiry, for ultimately the plant response, or yield, 

 is the index to favorable or unfavorable soil condition. 

 But the most significant fact is that in his most important 

 work the agronomist usually deals with these problems 

 in such a complex form that it is not possible to analyze 

 the result in terms of direct plant response. Just as the 

 agronomist's work is important, however, in securing such 

 general results, that of the physiologist is important in the 

 attempt to simplify conditions, to analyze factors, and 

 ultimately to determine the nature of the plant response. 



72. The ash content of plants. It has been noted 

 that water constitutes ordinarily about four fifths of the 

 weight of herbaceous plants. The remainder is solid 

 matter. When the latter is burned in an open fire, the 

 organic products are volatilized, and most of the mineral 



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