616 



SCIENCE 



[N. S. Vol. XXXVI. No. 932 



involving fertility and plant nutrition are 

 finally solved, I am inclined to think this 

 is the only means whereby we can hope for 

 success. At least the information derived 

 in this way is more apt to bring us to the 

 desired state of knowledge than our pres- 

 ent independent attitude. "The sciences 

 gain by mutual support," wrote Pasteur. 

 Certainly it is not by an arrogant assump- 

 tion to one's self that his particular science 

 is the "be all and end all" of human en- 

 deavor, that we shall gain any notion of 

 what is really happening in the soil and 

 what it all means ! 



George T. Mooee 

 ■Washington Univeksity 



TLANT FOOD IN RELATION TO SOIL 

 FERTILITY ^ 



I take it that the only justification for 

 me to review the subject of plant food in 

 relation to soil fertility or crop production 

 is the fact that recent publications from 

 the federal Bureau of Soils have strongly 

 afSrmed that there is no necessity of ap- 

 plying plant food in the restoration and 

 maintenance of soil fertility. Two prin- 

 cipal questions are raised: First, Does 

 plant food applied increase crop yields in 

 harmony with recognized soil deficiencies 

 and crop requirements? Second, Will the 

 rotation of crops maintain the productive 

 power of the soil by avoiding injury from 

 possible toxic excreta from plant roots 1 I 

 shall try to present facts and data and 

 exact quotations rather than my own opin- 

 ions concerning these questions of such 

 fundamental importance in relation to sys- 

 tems of permanent agriculture. 



In 1804 DeSaussure, the French scien- 

 tist, first gave to the world a correct and 

 almost complete statement concerning the 



' Presented at the Symposium on Soils at the 

 Washington meeting of the American Association 

 for the Advancement of Science. 



sources of the food of plants, including not 

 only the confirmation of Senebier's discov- 

 ery of the fijsation of carbon in the forma- 

 tion of carbohydrates, but also the evidence 

 of plant requirements for the essential 

 mineral elements secured from the soil. 



Sir Humphry Davy and Baron von 

 Liebig did much to popularize this infor- 

 mation during the following half century; 

 and they were followed by Lawes and Gil- 

 bert, whose extensive and long-continued 

 investigations furnished the needed proof 

 that the soil must furnish nitrogen as 

 well as the mineral elements; and finally, 

 only twenty-five years ago, Hellriegel dis- 

 covered the symbiotic relationship between 

 legumes and bacteria which gives access to 

 the inexhaustible supply of atmospheric 

 nitrogen for soil enrichment. 



Briefiy, it might be said that for nearly 

 a century the world of science has accepted 

 and taught, and the world of advanced 

 agricultural methods has practised, the 

 doctrine that soil fertility maintenance 

 and soil enrichment require the restora- 

 tion or addition of plant food, including 

 particularly phosphorus and nitrogen, 

 which are most likely to become deficient 

 in normal soils, potassium where needed, 

 and sometimes lime or limestone, which 

 always supplies calcium, and magnesium 

 as well if dolomitic limestone be used. Of 

 the other five essential elements, carbon 

 and oxygen are secured from the carbon 

 dioxid of the air, hydrogen from water, 

 and iron from the inexhaustible supply in 

 the soil; while the sulfur brought to the 

 soil in rain and otherwise from the at- 

 mospheric supply, resulting from combus- 

 tion and decomposition of sulfur-bearing 

 materials, supplemented by the soil's sup- 

 ply and by that returned in crop residues, 

 appears to be sufficient to meet the plant 

 requirements and the loss by leaching. 



After nearly a century of the increasing 



