1 BuBEAu OP Ageioxtltxjbe. 155 



Agricultural Experiment Station regarding the proper 

 maintenance of soil fertility and the more rational and 

 sensible use of fertilizers and the principal sources of 

 plant food. I cannot find in our more recent bulletins 

 and circulars anything that in essence, at least, was not 

 set forth in this Bulletin No. 140. Dr. Hopkins' epoch- 

 making book entitled "Soil Fertility and Permanent Ag- 

 riculture," which appeared in 1910, presents at greater 

 length and in a more detailed way essentially the same 

 ideas that are contained in our Bulletin 140, and, in my 

 opinion, all of our later day teachings in this State re- 

 specting soil fertility, and the general subject of soil 

 amendments are traceable to these two publications and 

 to the work of the Ohio Experiment Station. Since that 

 time, Professor Eoberts, as agronomist of the Experi- 

 ment Station, has enlarged somewhat on- these ideas in 

 his publications and lectures. The essential facts, how- 

 ever, are the same. These ideas have been confirmed by 

 his recent work on a number of experimental fields in 

 various localities throughout the State. As far as I am 

 able to gather from his writings and utterances, his be- 

 lief is : 



First. That no system of cropping should be fol- 

 lowed that wUl continually remove from the soil the ele- 

 ments of plant food without the return to the soil of crop 

 residues and manure made by feeding the crops removed 

 or without a systematic rotation containing leguminous 

 crops and cover crops. 



Second. That practically all of the soils of the State 

 contain inexhaustible quantities of potash, which through 

 the maintenance of the humus content of the soil can be 

 brought into available form sufficiently rapidly to meet 

 the potash requirements of farm crops. 



Third. That with the exception of the soils of the 

 Blue Grass region, the soils of the State are deficient 

 in phosphorus and that, therefore, this element should 

 be supplied in most instances most advantageously in the 

 form of acid phosphate until organic matter is restored 

 to the soil, after which rock phosphate may be used. 



Fourth. That the farmers of the State cannot af- 

 ford, in most instances, to buy nitrogen, but must obtain 

 this important element along with humus, by returning 



