254 SCIENTIFIC AND PRACTICAL AGRICULTURE. 



an acre of land, one per cent, is added to the soil, if the ploughing 

 is ten inches deep, or two per cent, if only five.) 



What is the prevaihng rotation of crops in England called? 

 436. What is this* course? 436. To what soils is it adapted? 

 436. How is the advantage of this rotation explained? 436. 

 What rotation is there preferred for heavier soils? 436. 



What are two important points of difference between English 

 and American agriculture? 437. Does English usage therefore 

 throw much light on our course ? 437. 



If we look into the analyses of crops, do we see important dif- 

 ferences in their requirements ? 277, Table V. In the absence 

 of fixed rules, settled, as in European countries, by long practice^ 

 what general rule should guide us ? 437. 



