No. 6 DEPARTMENT OF AGRICULTURE. 681 



moisture and sufficiently loose for the development of tubers, or 

 which is capable of amendment in this respect. Experience and ob- 

 servation combine to convince me that the control of soil moisture 

 is the great problem in farming, and it is true in an especial degree 

 in respect to potato-growing. 



Underdrainage. — If the land is naturally heavy and w^et, under- 

 drainage is required. There are few crops whose cash returns jus- 

 tify the expense of underdrainage in higher degree than the potato. 

 If a soil would become fitted for this crop by drainage, the work can 

 be safelj' advised, even for those w^ho might find it necessary to bor- 

 row the money for the work. This is not the place for direction con- 

 cerning drainage, but so many failures in potato-growing are due 

 to an excess of water in the soil, that em]thasis is placed upon the 

 importance of underdraining any wet land that is to be given the 

 costly seeding and tillage of the potato. The only first class ma- 

 terial for underdrains is tile, and in most clayey sections of the 

 country the yield of potatoes will increase with the extension of the 

 use of drain tile. 



Humus. — The control of moisture, however, is not secured in most 

 soils merely by drainage. Deficiency in a supply at critical times in 

 the growth of the plant is a usual cause of failure. In preparing a 

 soil for potatoes, a leading aim should be to increase its capacity for 

 storing moisture by the incorporation of rotted organic matter with 

 it. The soil may be regarded as a big sponge for the holding of 

 moisture, and its retentive character is fixed largely by its percent- 

 age of decayed vegetation. If a soil be clayey and deficient in humus, 

 the water from rains runs off it or is evaporated from its surface, 

 while the particles of clay ad'here to each other, holding little water 

 in a form friendly to plant growth. If a soil is sandy, the w^ater 

 from rains rapidly descends and passes away through the subsoil. 

 Either class of soils is greatly benefited by the presence of decayed 

 vegetation which stores moisture for future use of plants. Natural 

 potato soils are rich in humus, and other soils must be made to ap- 

 proach them in character by the use of humus-making material. 



The reader may have learned from excellent authonties that choice 

 tubers are secured from land nearly free from humus, and it was 

 formerly claimed by some that such land should be selected for this 

 crop, but it was found that good yields could not be gotten in dry 

 seasons without irrigation. 



After six years experimentation with potatoes, the Cornell Experi- 

 ment Station has reached this conclusion (Bulletin 196): "Where the 

 soil is in proper physical condition the moisture may be conserved 

 through an extreme drouth by means of frequent shallow surface 

 tillage. But if the soil has become deficient in humus no amount 

 of tillage is able to make good the deficiency. 

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