PERMANENT AGRICULTURE 13 



tilizing the soil which have in view only the effect upon the immediate 

 crop and which commonly apply less phosphorus per acre than the 

 crops remove during each rotation ; with the result that at the end of 

 the twenty-year period, there is a depletion instead of an increase in 

 the total phosphorus content of the soil. 



DIFFERENCES IN SOILS RECOGNIZED 



Another characteristic feature of the Illinois system of permanent 

 soil fertility is that it recognizes the differences in soils. It takes into 

 consideration the fact that they differ in physical character and in 

 chemical composition, and that their treatment must vary according 

 to these differences. In the beginning of Dr. Hopkins' work, there- 

 fore, the necessity for a thoro knowledge of all the soils of the state 

 was apparent, and a survey of the soil types of the state was com- 

 menced and is still going on. Among other things, this survey aims 

 to determine what the character of these types is, both chemical and 

 physical; what constitutes the differences between one type and an- 

 other ; where the different kinds of soils are to be found, together with 

 their exact location and boundaries. 



Realizing still further the necesssity of recognizing the differences 

 in soils, experimental fields were established and are still maintained 

 by the Experiment Station on varying types of soils, in order to test 

 out, by means of growing crops, the different systems of soil treatment, 

 and to learn how the soils respond in crop production to applications 

 of different elements of plant food. These fields are, by long-time 

 leases or by deed, devoted permanently to these soil experiments; so 

 that with the lapse of time, the effect of the system on the permanency 

 of the improvement in the soil will become known. 



Two systems of farming have been in operation on many of the 

 experiment fields. One is called the live-stock system and the other, 

 the grain system. The object of maintaining these two systems is not 

 to determine whether one is better than the other, but rather to de- 

 termine ways to maintain the fertility of the soil under either system. 

 The grain system is applicable to the great grain-growing areas, where 

 almost all the grain is sold from the farm, none being fed to live stock 

 and no manure made. It consists in substituting for manure the use 

 of leguminous catch crops, all crop residues being plowed under. The 

 live-stock system includes the use of manure in such amounts as can be 

 made from the crops grown. Under either system, the crop rotation 

 and the supply of minerals are the same, the humus and nitrogen of the 

 soil are maintained in about the same amounts, and the crop yields 

 obtained are also the same. 



