SOIL AND TILLAGE. 53 



take up nitrogen, potash, phosphoric acid, calcium, hydrogen, 

 carbon, oxygen and many other things, but the agricultural 

 chemist has instructed you that the first three are the only ones 

 the plants find it difiicult to obtain in abundance. He tells you 

 that usually the soil lacks some one or all of these, and you dress 

 the land with manure or buy fertilizers to supply them. Now, 

 let us see if they are really lacking. 



The results of 49 analyses of soils in some ten states for a 

 period of years as gathered and averaged by Professor Roberts, 

 late Director of Cornell University Agricultural Experiment Sta- 

 tion, give the following as the amount of these elements known 

 to be in the first eight inches of surface dirt in an acre of land. 

 Nitrogen, in round figures, 3,000 pounds ; phosphoric acid, 4,200 

 pounds ; potash, 16,000 pounds. This does not take into account 

 what may be locked up in the coarse sand and gravel, perhaps 

 40% more. (The soil was sifted with a fifty-mesh-to-the-inch- 

 sieve.) Neither does it take into account that which was con- 

 tained in the lower soil and subsoil, perhaps half as much more. 

 But we are sure that there is at least as much of these materials 

 in the first eight inches of average soil as would be placed there 

 by the application of 75 tons of average commercial fertilizer. 



Take another set of figures : The average wheat crop for this 

 country is around 14 bushels per acre. Now, 14 bushels of 

 wheat require about as follows : nitrogen, 30 pounds ; phosphoric 

 acid, 10 pounds ; potash, 14 pounds. Hence, the amount of 

 actual chemical fertility w^hich these analytic tests discovered to 

 be in the first eight inches of soil provide enough nitrogen for 

 one hundred years, enough phosphoric acid for 400 years and 

 enough potash for 1,000 years for the growing of wheat 

 annually at 14 bushels per acre. So much for theory. As a 

 matter of fact, we know that in actual practice we cannot go at 

 it in any such way as this, yet these figures should certainly make 

 us pause and inquire further into this mystery. Evidently the 

 chemical elements found are not "available," are not readv for 

 plant food. How then, can we unlock this store-house of 

 wealth? At present we are like Robinson Cruso sitting upon his 

 bags of gold "Pieces of Eight," utterly unable to get any com- 

 fort or nourishment or profit out of it. 



\Miat does the plant require of the soil besides these ele- 

 ments of fertility in abundance, plus moisture and humus? It 



