137 



Rogardiiis tho sooond quostion. we do not know as yet what dopth of soil 

 should ln> usod in comiiutatidus rolatins to tho elenuMits of soil fortuity, but 

 from what nioajior data wo have thus far obtained I question if. in our connuon 

 soils and with our oonnnon crops, wo can draw plant food in significant amounts 

 from depths below IS inches. In most soils with whicli I am familiar it has not 

 boon found protit:il>le to jilow deoitor than 7 inches. ;ind luM-anso of this I wish 

 first to consider tlie total stoclc of i)lant food in tho surface 7 inches of soil; and 

 because 1 have less knowledge of soil conditions elsewhere I shall confine myself 

 mainly to Illinois soils in this discussion. 



It should be understood. ht)wover. that Illinois soils are probably as rich as those 

 of other States with similar climate and latitude. This is strontjly indicated 

 by the Government statistics relating to tho corn crop. About 1 ,2(i().(»O(),000 

 bushels of corn (one-half of tho corn crop of the United States .and more than 

 one-third the total corn crop of the world) are produced annually in the five 

 f:;tates — Illinois. Iowa. Xol)raska, Kansas, and Missouri. The State of Illinois, 

 with one-sixth of tlie combined area of those five States, produces one fourth 

 of this corn. Illinois not only iiroducos mor(> corn than any otlier sin.i,'le State, 

 but according to tlie (Jovornment averages for the past ten years the yield per 

 acre in Illinois is fi-om 2 to 1:5 bushels higher than in tho other corn-I)elt States. 



Five great soil areas comprise tho l.-irger jiart of the Illinois corn lu'lt. These 

 areas are known as the Middle Illinois (ilaciation, the Upper Illinois Glaciation. 

 tho Pre-Iowan Glaciation. tho Early Wisconsin Glaciation. and the Late Wis- 

 consin Glaciation. More than one-half of tho State of Illinois is included in 

 those five soil areas. Tho i)rinciital typos of soil in each of those groat areas 

 have been carefully investigated, and I shall consider hero an average which 

 represents the conmionest soil in tiie Illinois corn belt — soil which in normal 

 seasons prodni-es ('.(t Iiushels of corn, CO bushels of oats, and ?>0 bushels of wheat 

 per acre, without tlie u.so of manure or fertilizers. In discussing tho average 

 composition of this soil I shall not consider tho element nitrogen, except to say 

 that wo do not and can not profital>ly raise corn on commercial nitrogen, and to 

 rennnd us that, at commercial prices, there is more than .$!().( M)().(i()() worth 

 of nitrogen resting on every acre of the earth's surface. Furthermore, there is 

 an actual profit in raising such crops as clover, stock peas, soy lieans. and alfalfa 

 for their own value, aside from tho value of tho nitrogen which they fix. The 

 general farmer may sometimes buy water, but he ought never to Imy nitrogen. 

 Aside from its use in intensive farming, as on high-i)riced land near large cities, 

 tho element nitrogen has no justified connnercial value. 



I wish to consider the phosphorus and tho potassium in this Illinois corn-belt 

 soil : 



In an acre of this soil to a depth of 7 inches, which is estimated to weigh 

 2,000,000 pounds, there are less than 1,200 pounds of phosphorus and more than 

 ,''.(;,000 pounds of potassium. If we could draw upon this plant food- for 100 

 bushels of corn each year, the phosphorus would be entirely exhausted in loss 

 time than is measured by the life of one such man as Col. N. B. Morrison. The 

 second 7 inches of soil contains less phosphate than the first, for our rich, 

 loamy soils contain in tho surface stratum some organic phosphorus, a part of 

 which has certainly been brought from tho second 7 inches l)y the vegetation 

 whi<'h has grown during past centuries. 



The 3G,000 pounds of potassium contained in the first 7 inches of soil are 

 sufficient to supply potassium for a 100-bushel crop of corn each year from 

 the birth of Christ until the present time, assuming that tho grain only is sold 

 from the farm. In the second 7-iuch stratum the supply of total potassium is 

 sufficient for another 1900 years. If the surface of the soil is washed away so 

 that the general level of the cultivated land is lowered at the rate of 1 inch 

 in 800 years, then our supply of potassium is absolutely permanent for a system 

 of practical agriculture of unlinntod application. 



Regarding the third question, it should be noted that much ignorant and 

 unjust criticism has been ofi:ered because the chemist is not able to determine 

 at any given time how much available plant food the soil contains and how 

 much'the next crop will be able to secure fi'om the soil, and because different 

 chemists have employed different methods in trying to get some measure of 

 the plant food which is likely to become available some time, but have not 

 found any one method which gives all of the information desired. 



The soil-fertility question in which mankind is most interested is not. How 

 much so-called available plant food does the .soil contain at any given moment? 

 but rather. How much total plant food does the soil contain and how can we 

 best make it available? By chemical methods, and by no other, can we ascer- 

 taiu the total stock of plant food in the soil to any given depth. Chemistry 



