Care of the Groioing Crop 167 



tion of plant-food, maintenance of healthful soil conditions, 

 saving moisture and weed killing that it must be practiced 

 after planting the potato crop. As the potato plants are 

 more tender than most weeds, great injury may result from 

 careless tillage. The tender white sprouts starting from 

 the seed tubers are usually injured by a touch. The soil 

 about the seed may be thoroughly stirred with a harrow 

 and level during the first few days after planting without 

 danger. The weeder can be used with good results in 

 killing weeds and keeping a soil mulch above the plants 

 if great care is used to prevent the teeth from injuring the 

 sprouts. If the number of injured sprouts is small, the gain 

 from the tillage may outweigh the setback which the in- 

 jured plants receive. 



The next period, from the time the plants form green 

 leaves above the ground till the tops are eight to twelve 

 inches high, is one when the benefits of tillage are usually 

 greater than possible injury. During a large part of the 

 time the plant-food in the seed tubers is still available, and 

 the leaf surface is not yet large enough to transpire enough 

 water to seriously injure the plant. Sun-scald and tip- 

 burn are not common until the plants are larger. Roots 

 are being developed close around the seed and stalks. 

 Until the roots are numerous enough for tillage to destroy 

 more than a small proportion of the whole root system, 

 tillage is beneficial. Later the horizontal roots extend 

 until they cross between the rows. These roots are now of 

 the size to make their injury a serious matter to the grow- 

 ing plant. The greatest development of the roots is in 

 the plowed area, or five to ten inches below the surface. 

 Many roots also extend down to the depth of three to four 

 feet. A large part of these vertical roots drop downward 

 from the large horizontal roots close to the surface. It is 



