410 FIELD CROPS 



and destroy all weeds without injuring the roots of the pota- 

 toes. On deep, rich, well-drained land, the potato roots are 

 likely to grow so deep that thoroughly good cultivation 

 may safely be given to a depth of from 2 to 3 inches. Culti- 

 vation may be continued until prevented by the spread of 

 the vines. The later cultivations are usually given with a 

 one-horse, fine-toothed cultivator. 



556. Irrigation. As the potato crop gives large returns 



to the acre, it is quite commonly grown on irrigated land. 



The method of planting in drills also greatly facilitates the 



process of getting water to the crop. Extremely large yields 



of potatoes are obtained under irrigation; in fact, with the 



exception of Maine, the states producing the largest average 



yields per acre are those in which the main part of the crop 



is irrigated. 



HARVESTING AND STORING 



557. Harvesting. As a rule, potatoes are not harvested 

 until they are ripe; that is, until the vines are entirely dead. 

 High prices, however, may make it profitable to dig early 

 potatoes before they are fully mature, even though a smaller 

 yield is obtained. Where only a small acreage is grown, the 

 crop is commonly dug with a fork, the potatoes from two 

 rows being thrown together. Potatoes may also be plowed out 

 with a common plow. The potatoes that are thus exposed are 

 picked up; then the land is harrowed and others are brought 

 to the surface. Tliis method, however, is not in general use, 

 because all the potatoes are not obtained. Where large 

 acreages are grown, a four-horse potato digger is commonly 

 used. This machine is equipped with a broad, sharp point 

 which runs under the row and carries the earth, vines, and 

 potatoes over a chain elevator through which the earth falls, 

 leaving the potatoes to be dropped behind. There are sev- 

 eral different types of potato diggers, but all work on approx- 

 imately the same principle. Digging by machinery is by far 

 the most satisfactory where there is much digging to do. 



