THE VEGETABLE GA&DEN 323 



once in the soil must be starved out by growing on the infected field 

 other crops, such as grass or grain, for several years. In certain 

 localities in the central part of the United States and elsewhere the 

 following three years' rotation has given highly satisfactory results 

 on farms where potatoes are extensively grown ; Fall wheat, in which 

 clover is seeded in the spring; second year, clover, plowed under in 

 fall or winter; and third year, potatoes. In some localities the un- 

 certainty in obtaining a catch of clover renders this rotation inex- 

 pedient. 



Detailed directions for the preparation of one class of soils would 

 not apply to others, hence it can only be said that preparation should 

 be deep and thorough, and that unnecessary compacting of the soil 

 should be avoided. Plowing can scarcely be too deep, provided that 

 much of the subsoil is not brought to the surface ; when practicable, 

 the depth should be gradually increased from year to year. Though 

 the tubers are usually formed within 6 inches of the surface of the 

 ground, the roots feed deeper. Practical experience, as well as the 

 extent of the distribution of potato roots in the soil, emphasize the 

 importance of deep and thorough preparation of the soil for this 

 crop. Whether fall plowing is advisable depends on a variety of 

 local considerations. In general in a mild climate fall plowing of 

 light land exposes it to leaching; on the other hand, fall plowing is 

 sometimes necessary, as, for example, when a field is badly infested 

 with injurious insects. 



Fertilizing. The potato requires liberal manuring. Barnyard 

 manure usually affords a large increase in the crop, for not only does 

 it supply nitrogen, phosphoric acid, and potash, but it improves the 

 mechanical conditions of the soil. However, its direct application to 

 the potato affords conditions favorable to potato diseases, and thus 

 injures the quality of the crop. For this reason the best practice is 

 to apply barnyard manure to corn or grass the year before the po- 

 tatoes are grown. If it is considered necessary to apply it directly 

 to the potato crop it should first be well rotted. 



If for several years before potatoes are planted the land has been 

 properly manured with farm manures, or with green crops plowed 

 under, commercial fertilizers can be advantageously used on most 

 soils. Generally, a complete fertilizer should be used i. e., one 

 which contains nitrogen, phosphoric acid, and potash. The farmer 

 is justified in supplying all three of these fertilizing ingredients, 

 unless by previous tests he has learned that on his soil a certain one 

 of them can be safely omitted. Of nitrogenous fertilizers, one of the 

 best for potatoes is the quick-acting nitrate of soda. Of phosphatic 

 fertilizers, superphosphate is preferred. Among potash fertilizers 

 the sulphate of potash has been found to afford a better quality of 

 potato than kainit and muriate of potash. Ashes, are extensively 

 and effectively used to supply potash to potatoes. 



As little farmyard manure is available in the Southern States 

 where the early crop of potatoes is chiefly produced, this seldom en- 

 ters as a factor in the production of the crop. Commercial fertilizers 

 of a nature especially adapted to the potato crop form the chief re- 



