568 VARIOUS FERTILITY FACTORS 



about 20 borings taken from as many different places where the 

 soil appears to be uniform and truly representative of the soil type) 

 and employ a skilled chemist to determine the total phosphorus and 

 total nitrogen, and in case of naturally poor or abnormal soils it is 

 well, also, to have determinations made of the total potassium, total 

 magnesium, and total calcium. 



The chief value of a chemical analysis is not to serve as a guide 

 in the application of some certain plant-food element in readily 

 available form for the special benefit of the next crop, but rather to 

 serve as an absolute foundation upon which methods of soil treat- 

 ment can be safely based for the adoption of systems of permanent 

 soil improvement. 



Thus, if the plowed soil of an acre is found to contain 810 pounds 

 of total phosphorus and 47,600 pounds of total potassium, as is the 

 case with the yellow-gray silt loam of the late Wisconsin glaciation, 

 the most common upland soil in Lake County, Illinois, then a 

 system of farming which will increase the phosphorus content of 

 the soil and which will liberate potassium from the practically 

 inexhaustible supply will certainly rest upon a practical and truly 

 scientific foundation, notwithstanding the fact that in actual 

 trials the application of soluble potassium salts in the absence of 

 sufficient decaying organic matter might produce a marked effect 

 on crop yields, as in the case of wheat in the Rothamsted experi- 

 ments. 



In practical agriculture the first soil test should be that for acid- 

 ity, and if acidity is found in the surface and more marked acidity 

 in the subsoil, the first treatment should be the application of 2 

 to 5 tons per acre of ground limestone. Following this, clover or 

 some other legume should be grown, inoculation being provided, 

 if necessary, and liberal supplies of decaying organic matter should 

 then be provided by plowing under the clover either directly or 

 in the form of manure. Next, some form of phosphorus should be 

 added with the organic matter, more especially to note its effect 

 on the yield of succeeding crops of legumes. Finally, if necessary 

 or desirable, some soluble salts may be applied, such as potassium 

 chlorid, sodium chlorid (common salt), kainit, or calcium sulfate 

 (gypsum or land plaster), to note whether such addition would 

 produce at least temporary profit until the supply of decaying 



