462 Kansas State Board of Agriculture. 



ALFALFA'S EFFECT UPON THE SOIL. 



By J. T. WILLARD, Dean of the Division of General Science and Professor of Chemistry, 

 Kansas State Agricultural College. 



The most imperative duty of all cultivators of the soil is to conduct 

 their art in such a manner as to conserve fertility. The world can no 

 longer send its waves of surplus population over unpeopled areas or 

 against savage aborigines. At least if the foregoing is not literally true, 

 it will be within a century, and at the present time the effect of di- 

 minished returns from the soil must be corrected by treating the soil, 

 not by abandoning it and exploiting fresh areas. 



That crops, differ in their effect upon a soil is well known, and the 

 benefits following seeding to grass, especially if clover accompanies it, 

 and from growing clovers alone, have been known from time immemorial. 

 There are several elements that participate in the general results, and a 

 clear recognition of these is not always made by practical men. Lack of 

 knowledge on some phases of the practice leads to misapplication of 

 effort, and misunderstanding of the results obtained. To set some of 

 these considerations in a clear light is the object of this article. 



All crops take up from the soil certain chemical elements necessary 

 to their growth. These are deposited in the roots, stems, leaves and 

 seeds, and in so far as these parts are removed from the land it suffers 

 a loss of the absorbed material. Some of the elements in plants come 

 from the air, and of these there is thus an amount available that is prac- 

 tically unlimited. The carbon, oxygen and hydrogen of plants are fur- 

 nished chiefly by carbon dioxide in the air, and water in the air and soil. 

 The nitrogen of plants may be traced to the atmosphere as its original 

 source, but the soil contains the immediate supply of this element for 

 most species of plants. The phosphorus and sulphur which plants con- 

 tain comes entirely from the earth, and the same is true of the metals, 

 iron, sodium, potassium, magnesium and calcium. In considering the 

 problem of the fertility of the land, the chemical elements usually con- 

 sidered are calcium, potassium, phosphorus and nitrogen. The residue 

 from plant or animal life existing as the humus or organic matter of 

 the soil is of high importance also. This contains much carbon, and 

 more or less of all of the chemical elements which enter into the plants. 



The purpose of crop production is to obtain something that may be 

 removed from the soil and converted to the use of man. Any crop that 

 is raised merely to be plowed under is a means to the general end of ob- 

 taining something that may be removed. It is this removal of material 

 that lies at the foundation of soil exhaustion. Unfortunately agricul- 

 tural operations also cause loss of material that never gets into the 

 crops. The relation of alfalfa-growing to soil fertility will now be pre- 

 sented in the light of the foregoing fundamental considerations. 



Alfalfa is commonly classified as a legume, and belongs to one of the 

 most important families of plants, many species of which are of great 

 economic value to man as sources of food for himself or domestic ani- 



