SYSTEMS OF CROPPING 87 



2. Grain crops and many others take all their nitrogen 

 from the soil; but leguminous crops, such as the clovers, 

 peas and beans, gather much nitrogen from the air in the 

 soil. Their growth will increase the store of nitrogen in the 

 soil. A rotation of crops which includes the legumes will 

 help to keep up the nitrogen supply in the soil. 



3. Crops put waste matter into the soil through their 

 roots. This often acts as a poison to the kind of plants that 

 put it there. It may not be a poison to other kinds of crops 

 which follow in the rotation. 



4. Soils should be covered with growing crops as much of 

 the time as possible. This guards against loss of soil by 

 washing and leaching. It is possible to keep the soil thus 

 protected if we have a rotation of crops; but it is usually 

 not possible if but one crop is grown. 



5. Insect enemies and diseases of plants are liable to be 

 worse when one crop is grown continuously. Rotation of 

 crops is often a perfect remedy against these enemies. 



6. There is more continuous work for men and horses, 

 because a rotation of crops distributes the labor throughout 

 the season. Horses and men should be given steady employ- 

 ment if possible. It is not profitable to keep horses idle too 

 long at a time, as when only one crop is raised. 



7. Rotations always require a variety of soil treatment, 

 as plowing the ground at different times of year. This is 

 better than alw^ays following the same tillage at the same 

 season of the year. We can best control the soil moisture 

 by proper tillage at the right season. 



8. Rotation of crops helps to keep weeds in check. Many 

 weeds which thrive in a hayfield will be kept down by a 

 culture crop, as corn, cotton, or potatoes; while certain other 

 weeds, which are bad in a cornfield, may be killed by growth 

 of grain or grass. 



9. More sources of income are found on those farms where 

 rotations are practised. There is also less danger of financial 



