Climate, Soils and Rotation 89 



rapidly rising in price, and methods of increasing the yield 

 of crops will become more important than before. 



The high cost of labor in the United States compared 

 with that of land has resulted in the invention and use 

 of labor-saving machinery for nearly every process of 

 farming by which the power of horses or of engines has 

 displaced that of human muscle. Machinery cannot so 

 much increase the production to an acre as the production 

 to each worker engaged in farming by increasing the num- 

 ber of acres farmed by each. For example, the use of 

 horse-drawn tools compels a wider spacing of potato 

 rows than where most of the work is by hand labor. 

 This reduces the yield to the acre by reducing the num- 

 ber of plants. On the island of Jersey, rows of potatoes 

 are spaced 16 inches apart and 24 to 27 in other parts of 

 Exu-ope, compared with 33 to 42 in America. 



FACTOKS INFLUENCING POTATO CULTURE 



Study of the factors governing the choice of methods 

 for the culture of the potato shows that eight are of prin- 

 cipal importance: (1) heat in air and soil; (2) water; 

 (3) soil texture; (4) available plant-food; (5) drain- 

 age and soil air; (6) the "critical period" in the life of 

 the plant; (7) type, variety and strain of the seed; 

 (8) diseases. 



The term "limiting factor" is frequently used in other 

 connections and is peculiarly appropriate in potato- 

 growing. Any one of the above factors may be inhibiting 

 in some conditions and may be able to place a limit on 

 the size of the crop which cannot be removed by the 

 others being favorable. For example, all farmers are 

 familiar with the loss of yield caused by drouth, although 



