SOIL FERTILITY 329 



forage and cover crops and small grains for necessary feed 

 for farm animals. 



Principles of rotation. In the southern states as a 

 rule it will be found much more profitable to grow a crop of 

 cotton or tobacco once every three, four or five years on the 

 same field than every year. There are four kinds of crops 

 that should be considered in every rotation. First, a ready- 

 money crop, and upon this crop the rotation should be 

 based. In the South these crops are usually cotton or to- 

 bacco, sometimes wheat. Second, there should always be 

 a fodder crop available for necessary feeding of farm ani- 

 mals. Third, there should be at least one legume in the 

 rotation in order to furnish humus for plant growth. 

 Fourth, in every rotation there should be a plan for the 

 growing of a winter cover crop to prevent the erosion and 

 leaching of the soils. The latter is especially important in 

 the southern states. 



In working out a system of rotation no plan will be safe 

 to follow for all states or all districts. It is therefore quite 

 important that the farmer should consult the local experi- 

 ment station and college of agriculture with reference to 

 a suitable system of rotation. In general, the following 

 principals of rotation should be carefully considered: 



Rotation Rules. 1. Rotate the crop so as to give not 

 less than one money market crop every year. When 

 plenty of land is available, two or more money crops 

 should be grown. 



2. Rotate crops so as to have as much green feed as 

 possible for the entire year. 



3. Rotate the crop so as to make use for each suc- 

 ceeding year of the remains or residue of former crops, 

 such as manures and other fertilizers. 



4. Rotate the crops so as to secure as much nitrogen 

 as possible from the air. Clover, alfalfa, cow-peas and 

 other legumes will do this. 



