No. 6. DEPARTMENT OF AGRICUDTUP^E. 185 



The psychist and biologist have important duties to perform in 

 their field of service. Chemistry unaided cannot solve the prob- 

 lems that arise. It is, however, to the chemical side of certain soil 

 questions that I wish to direct your attention. 



Analysis has discovered the fact that plants contain many of the 

 elements present in the soil, and experiment has proven that in 

 order to grow and perform its full range of functions the plant 

 must find in the soil water to drink and oxygen to breath, and from 

 it must also obtain a suitable supply of nitrogen, potash, lime, mag- 

 nesia, iron, phosphoric and sulphuric acids; and that, in addition 

 to these materials, it usually takes uj) from the soil more or less 

 soda, nuniganese, chlorin, silica and carbon, but, strangely, that 

 alumina, abundant in the soil, is rarely found in plants. Experience 

 has further shown that in most well-managed soils crops are sure 

 to find suitable supplies of all essential food elements except nitro- 

 gen, phosphorus and potassium, but that many soils, otherwise fer- 

 tile, are deficient in the elements last named, either in point of 

 quantity or of fitness for the plant's consumption. Hence, the dis- 

 tinguished investigator, who has just preceded me on this program, 

 ventured, a few years since, to define agriculture simply as the art 

 of converting the nitrogen, phosphoric acid and potash of the soil 

 into the more valuable forms of grain, fruit, meat and milk. 



When chemistry was first applied to the study of farm problems, 

 it was supposed that, having at command the means of determining, 

 on the one hand, how much of each element the growing crop re- 

 quires, and. on the other, the exact quantity of the required element 

 present in the soil of a given field, the chemist could at once deter- 

 mine what food constituent, if any, was lacking, and what should 

 be given to the soil to make good the deficiency, thus saving the 

 farmer many a season of expensive experiment and many a dollar 

 of needless expenditure. It was soon found, however, that after 

 excluding cases in wliich the failure was probably due to physical 

 and i)i<)logic;il. ratlicr than to I'lircly rliemicnl. coiiditiouK, the solu- 

 tion of the remaining questions by the recognized chemical methods 

 was far more difficult than had been anticipated. Let us review 

 so,me of the steps chemists have taken in hope of gaining a satis- 

 factory basis of judgment respecting the chemical fitness of a soil 

 for the maximum production of a particular crop. 



When a rock or a mineral is to be analyzed, methods are selected 

 which will serve to separate completely all of each constituent from 

 every other substance present. It was recognized that plants effect 

 no decomposition so far-reaching. Accordingly, the action of boil- 

 ing concentrated hydrochloric acid was substituted for the more 

 drastic proces.'ses of mineral analysis. Even this method was not 

 used with the exyiectation that it would show precisely what a 

 given crop, or even a crop of average feeding power, could remove 

 from the soil in a single growing season. It was promptly recog- 

 nized, also, that by varying the time of action of the acid the tem- 

 perature, or the acid strength, results differing considerably with 

 respect to certain constituents, would be obtained. It was, at the 

 same time, clearly perceived that in different soils, or even in the 

 same soil, a single element might exist in several states of combina- 

 tion with other elements, each combination having its own character- 

 istic fitness or unfitness for consumption by plants. The method 



