442 FIELD CROPS 



thoroughly to all parts of the plant, and in strong enough 

 form to be sure to destroy the bugs. The use of a poor 

 grade of poison or of a weak solution may make the work 

 ineffective. Early and effective spraying is imperative. 

 Spraying for both blight and bugs may be accomplished by 

 mixing poison with the Bordeaux mixture, instead of with 

 water, and applying both at one operation. 



579. Rotations for Potatoes. Potatoes fit into a rotation 

 very much as corn does; that is, it is a good crop to follow 

 clover or grass and grain crops succeed well following it. 

 Grain crops are slightly more likely to lodge following a pota- 

 to crop, probably due to the fact that potatoes draw rather 

 heavily on the potash supply and leave the soil more mellow 

 and loose than corn. 



A very common rotation in the general potato-growing 

 sections in the North is: First year, clover; second year, 

 potatoes; and third year, grain. In this rotation the pota- 

 toes are planted on clover sod, and if available, a good appli- 

 cation of manure or commercial fertilizer is added. On light 

 or worn soils, such a rotation is desirable, at least until the 

 condition of the soil is greatly improved. In many cases, 

 soils thus cropped have become so enriched as to cause suc- 

 ceeding grain crops to lodge. The rotation may then well 

 be changed to a four-year system, introducing a crop of corn 

 following the potato crop. Such a rotation would then be: 

 First year, grain; second year, clover; third year, potatoes; 

 fourth year, corn. The two cultivated crops, corn and pota- 

 toes, usually draw heavily enough on the fertility so that the 

 succeeding grain crop will not grow too rank and lodge. 



In the South, the supply of vegetable matter is main- 

 tained usually by growing cowpeas or some other green 

 manure crop, preceding and following the potato crop. A 

 two-year rotation commonly followed is: First year, corn 



