CROPS AND FERTILIZERS 



ing proportions, and no two crops have the same 

 capacity for extracting difierent food elements 

 from the same soil. It is advantageous, then, 

 to follow a crop that requires, for example, a 

 large amount of potash by one that requires but 

 little of that particular constituent. Again, 

 deep-rooted plants should be followed by shal- 

 low-rooted ones. Then there are the nitrogen- 

 gathering crops (legumes) that have the abil- 

 ity to gather all the nitrogen they need from 

 the air; there are crops that have to take their 

 supply of nitrogen from the soil; and finally, 

 there are certain crops subject to attack from 

 parasitic fungi and insect pests; and as the fungus 

 and the insect that grow in and live off one 

 plant are powerless to thrive on others, they 

 can be held in check by the planting of different 

 crops in the same field in rotation. 



Where dairying is prominent, and where po- 

 tatoes are a profitable crop, an excellent rota- 

 tion would be: Potatoes, followed by corn 

 for two years (the first year for a matured crop, 

 and second year for silage) ; then grass and 

 clover for three years. This is a six-course ro- 

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