ROTATION OF CROPS. 89 



value of different crops, the facilities for marketing 

 them, the greater or less price of live-stock products 

 and the present money needs of the farmer, often 

 must determine the exact rotation he adopts. 



The alternation of grain'with green crops; of culti- 

 vated with uncultivated crops, are fundamental prin- 

 ciples in theoretical rotations. So far as maintaining 

 fertility is concerned it would probably never be best 

 to repeat a grain crop without an intervening green 

 crop, but in practice it is often best to cultivate the 

 same crop two, sometimes even more, years in suc- 

 cession. 



In Great Britain roots are the chief cultivated crop. 

 In the United States, Indian corn is the principal 

 cultivated crop. Unlike as maize and root crops are 

 in other respects this one point in common makes 

 each promiilent in the best systems of rotation in 

 the country in which they are grown. 



The "Norfolk" four course, or four years rotation, 

 has b(^n very popular on light land in England. The 

 order of cropping is: Roots; grain, usually barley; 

 "seeds," that is, a mixture of clover and grasses; 

 grain, usually wheat — each one year. The roots 

 are turnips, or mangels, and are often eaten by sheep 

 on the ground where they grew. Sometimes, clover, 

 rye, turnips, or vetches are sown after the wheat is 

 harvested and these crops followed by the regular 

 root crop. On poorer soils, or where it is not desired 

 to have a grain crop so frequently, the "seeds" may 

 be left two or three years, as is the usual practice in 

 this country. In some parts of England the rotations 

 are very elaborate, lasting several years and intro- 

 ducing a variety of "catch crops." 



