8o 



SOILS 



good deal of nitrogen but little phosphorus and potas- 

 sium, others using but little nitrogen but much phos- 

 phorus and potassium, and still others much potassium 

 but little nitrogen and phosphorus, and other plants us- 

 ing these foods in still other proportions. As individual 

 plants were studied, it was observed that some plants 

 used one or more food elements that each particularly 

 fancied, and while each used the other elements, it did so 

 very modestly, and, when compared with its favorite 

 dish, often very shyly, indeed. 



Some variations in food requirements. To prove that 

 these variations in food requirement are real, we need to 

 examine only a few plants just four of our leading 

 cereals. 



The table following shows these variations with four 

 crops each one being partial to a different combination 

 of food elements : 



This table shows that while corn is a heavy feeder of 

 nitrogen and potassium, it is certainly modest in its de- 

 mands on phosphorus. The table shows, also, that when 

 wheat and oats are compared, that the call for nitrogen is 

 practically identical with the two crops, but that oats call 

 for about 20 per cent, more phosphorus and no per cent, 

 more potassium than wheat. 



* On basis of average yield per acre in United States. 



