ROTATION OF CROPS. 95 



ment of the soil, we do not give the weeds so good a chance to 

 rob the crops and infest the fields. 



5. The insects also make their homes on certain crops and 

 in the ground. By rotating the crops we disturb the insects 

 and help to keep them in check. If we remove the food of 

 the insects, bury them or their eggs deep in the soil, or turn 

 them up to the frost we are helping to destroy them. 



6. Some crops mature early in the year, as fall wheat and 

 barley ; others late in the fall, as corn and roots. Some are in 

 the ground but a short time, others for a long time, and so 

 they have different lengths of time for feeding. It is often 

 helpful to have a long-feeding crop followed by a short-feeding 

 crop, as in the case of roots followed by barley. 



We may then sum up by saying that crops differ : 



As to the kind of food which they take up ; 



As to the amount of different foods which they take up ; 



As to the length of their feeding roots ; 



As to the length of time that they are feeding ; 



As to the treatment we give them (cultivated or not) ; 



As to the weeds that associate with them ; 



As to the insects that infest them ; 



For these and other reasons the best farmers always pay 

 careful attention to the proper rotation of their crops. 



SAMPLES OF ROTATION. Let us take what is called a four- 

 year or four-course rotation turnips, barley, clover, wheat. 

 The first crop requires thorough cultivation and gives a chance 

 to manure heavily for the entire course. Turnips are bi- 

 ennials, and therefore long-growing, feeding until late in the 

 year. Then comes a shallow-rooted, quick-growing crop of 

 an entirely different nature. The clover at once follows barley 

 and sends its roots deep. It feeds upon the free nitrogen 

 of the air in the soil through its root tubercles, and when 

 plowed in leaves a large quantity of material in the roots and 

 stubble to make food for the wheat. The manure applied with 



