NEW YORK, JULY 15, 1893. 



THE CHEMISTRY OF SOILS.' 



BT PROFESSOR R. ELLSWORTH CALL. 



A SOMEWHAT extended experience ia the chemical analy- 

 sis of soils with a view to their agricultural value has led 

 to certain conclusions which may not be altogether devoid 

 of value to the readers of Science. Especially may this 

 be true since there is often an entirely erroneous opioion 

 among those most concerned respecting' the useful deduc- 

 tions which may be made from a complete chemical analy- 

 sis of a soil. Usually it happens that if only the presence 

 of certain desirable substances be shown, then the value of 

 the soil for the production of this or that crop is assumed to 

 be definitely settled. Nothing could, in general, be farther 

 •from the truth. Of course, something definite may be said 

 of such soils as those in which both sand and clays, or 

 either, predominate, but the conclusions in these cases are 

 based on the physical characteristics of the soils rather than 

 on their chemistry. Indeed, it is usual to classify soils in 

 two general categories, the classification being based, on the 

 one band, on the method of soil-formation, and, on the other 

 hand, on its physical characteristics. The soils of Iowa be- 

 long, in the main, to that class which is based on the 

 method of formation, and are composed chiefly of transported 

 or drift materials. It is, however, true that the Iowa soils, 

 though glacial, owe much to the physical characters of the 

 rocks which they represent as disintegrated and far-travelled 

 debris. The sands and clays are all transported materials, 

 most of them from points many miles to the north of the 

 prairie regions which they now cover. It is, moreover, 

 clear that no degree of coarseness or of fineness, which may 

 result from the methods of origination of any soil, consti- 

 tutes in itself sufficient ground for saying this soil is fertile 

 or that soil is unsuitable for plant growth. Recourse must 

 be had to the ultimate composition of the sample, and right 

 here enters an element of error against which, popularly, it 

 is difficult to guard. 



The physical character of a soil or marl must be consid- 

 ered when studied chemically. The finer the condition of 

 the sample, in nature, the more readily are induced those 

 changes in its chemistry vrhich result from atmospheric in- 

 fluences. That is to say, when coarse and fine soils are 

 treated alike mechanically by the plow, the one may become 

 mellow and well mixed, while the other is broken without 

 being vvell mixed or turned. Now, the chemical processes 

 which occur are most active and most complete in soils that 

 are fine in texture. It follows, therefore, that a stitf, clayey 

 soil may contain all the essential elements of the food of any 

 plant, but be in such condition physically as to render the 

 chemical processes difficult of operation. And, on the other 

 hand, such a soil may be sufl3ciently fine, but the well-known 

 tendency to '"cake" or harden on drying or exposure would 

 render it valueless agriculturally, no matter how finely com- 

 minuted its inaieridls may be. 



1 Extracted from tlie Monthly Review Iowa Weather and Crop Service, 

 Vol. III., No. 5, 51ay, 1892. 



Clayey soils, again, do not permit that free, subsoil cir- 

 culation of water so necessary to growing crops. Circula- 

 tion there is, but it is limited at best; open, porous soils ad- 

 mit free, underground water-flows, but such soils soon dry. 

 They lose large quantities of water through evaporation, due 

 to the rather free circulation of air in the upper portions of 

 the cultivated areas. 



Color, too. has little to do with deciding finally whether 

 a soil will be fertile. Usually all earths which are dark- 

 colored or black — a condition largely due to the amount of 

 carbonaceous material derived from decayed vegetation — 

 are considered fertile. It is true that common consent places 

 all such samples among the fertile soils, but it by no means 

 follows as a necessary deduction. So, too, that light drab 

 or ashy-colored soils lack the elements of fertility is a notion 

 which observation and experiment alike negative. The most 

 fertile of Iowa soils is the loess, a peculiar and very fine 

 marl covering many hundred square miles along the Missis- 

 sippi and Missouri rivers, as well as the higher lands along 

 the Des Moines. It is a soil the color of which would con- 

 demn it for agricultural purposes, but it is one which is of 

 exceptional value for all sorts of cereals, and is peculiarly 

 adapted to the growth of fruit. It is finer in texture than 

 is any other soil in the State. What, then, constitutes its 

 peculiar feature, rendering it so valuable ? The answer to 

 the query lies almost solely in its physical condition, which 

 is of a fineness equalling that of any clay. This fine condi- 

 tion renders it admirably suited to the action of native 

 chemical agents. These are the real soil-makers. Soils that 

 plants may use must be soluble, and one of the essentials tO' 

 complete solubility is fineness of the constituent particles, 

 A certain and definite relation to moisture must be est^b' 

 lished and maintained, a condition which is practically 

 reached by under-draining soils of a clayey nature. Too 

 much water will compel adhesion of the smaller particles, 

 and the product thus formed be eventually coarse and 

 lumpy. Such a soil may be very fertile, but is not arable. 

 This is the condition of most of the bottom lands of eastern 

 Arkansas, the soils of which region are deficient in lime 

 alone of all the ingredients which plants require. They are 

 " wet and cold," and cannot be under-drained. Few soils 

 of this nature occur in Iowa. 



To make a long story short, chemical analysis of any 

 given soil will determine its probable agricultural value only 

 within very wide limits, and for reasons which appear be- 

 low. It may be said, at this time, that such an analysis 

 may determine one of two things, (a) the presence or ab- 

 sence of constituents which the plant must have, or (6) the 

 presence of some substance which will affect injuriously a 

 growing plant. The chemical laboratory will never sup- 

 plant the province of carefully conducted experimental ag- 

 riculture. But it may become a most valuable adjunct to 

 the operations of the farm. The principles which underlie 

 agricultural chemistry need ouly to be understood to be ap- 

 preciated by those who have the manual labor of the farm 

 to perform. 



Aside from these general considerations there remain yet 

 others to which it will be well to advert. 



