AVAILABLE PLANT FOOD 



in 



TABLE 21. ANNUALLY AVAILABLE FERTILITY IN ILLINOIS SOILS, ROUGHLY 

 ESTIMATED Continued 



SAND, SWAMP, AND BOTTOM LANDS 



1 The nitrogen in peat is so very slowly available that not even a rough estimate 

 can be made here. 



they first dissolve in the soil water and spread over the surface of 

 the soil particles before becoming insoluble, and thus they offer 

 a much more extensive surface for contact with plant roots than 

 would plant-food particles applied in insoluble form, unless very 

 finely ground. 



Third, we may apply different elements of plant food to the soil 

 and note the effect, if any, in increasing the yield of crops, and thus 

 sometimes discover what element is most deficient in the soil. 

 One might suppose that this would be the best method, but such 

 is not the case. This method frequently gives erroneous results 

 which, if followed, may lead to land ruin, because the substance 

 applied may produce little or no benefit on account of the special 

 plant-food element it contains, but it may act as a powerful soil 

 stimulant and thus liberate from the soil some other entirely differ- 

 ent element in which the soil is already becoming deficient. Thus 

 have many lands been practically ruined by the use of land-plaster 

 and salt, by the improper use of lime, and even by the use of clover 

 merely as a soil stimulant. Some good illustrations of this action 

 of soluble salts are shown in the following pages. 



"In considering the general subject of culture experiments for determining 

 fertilizer needs, emphasis must be laid on the fact that such experiments should 

 never be accepted as the sole guide in determining future agricultural practice. 



