THE ESSENTIALS OF A ROTATION 513 



of soil fertility, and while the cultivation tends to "burn out" 

 or hasten the decomposition of vegetable matter, it aids in 

 the changing of plant food from insoluble to soluble forms 

 and also conserves moisture. Intertilled crops include corn, 

 cotton, potatoes, sugar beets, tobacco, and many others of 

 less importance. The annual leguminous forage crops may 

 be cultivated like corn or sown broadcast. Their effect on 

 the soil is very similar to that on other crops, except for 

 their ability to add nitrogen. 



670. The Essentials of a Good Rotation. The essentials 

 of a good rotation are : 



An intertilled crop, 



A crop for cash returns, 



A crop for feeding to live stock, and 



A crop to increase the supply of vegetable matter and 



nitrogen. 



Two or more of these essentials may be embraced in a single 

 crop. Thus clover supplies a crop for live stock feeding, 

 and is one which increases the supply of humus and nitro- 

 gen. Corn is a cultivated crop, and may be either a cash 

 crop or one for feeding to live stock. 



671. An Intertilled Crop. As already stated, weeds 

 increase when grain crops are grown, and the methods of 

 destroying them are limited. Some classes of weeds increase 

 in meadows and pastures. An intertilled crop is needed at 

 intervals to subdue weeds and to keep them from over- 

 running the land. Tillage aids in retaining the soil moisture 

 and in liberating supplies of plant food. Stirring the soil 

 allows the air to penetrate to the roots of the plants and 

 enables them to grow better than in hard, cloddy ground. 

 The aeration of the soil also improves its texture and pro- 

 vides more favorable conditions for the growth and work of 

 some of the beneficial bacteria. 



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