ROTATION OF CROPS 483 



and alfalfa. These remain on the land for two or more 

 years and increase the supply of vegetable matter by the 

 mass of stubble and roots which they produce. All annual 

 crops not intertilled will be designated in this discussion as 

 grain crops. They are sown too thickly to allow intertillage, 

 and occupy the land but a few months. They exhaust the 

 supply of humus and plant food elements, and are also 

 exhaustive of soil moisture. This class of crops includes 

 wheat, oats, barley, rye, flax, buckwheat, millet, and all 

 annual forage crops similarly produced. Intertilled crops 

 are planted in rows wide enough apart to be tilled during a 

 large part of the growing season. They are also exhaustive 

 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. 



662. 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. 



663. An Intertilled Crop. As already stated, weeds 

 increase when grain crops are grown, and the methods oi 



