268 IRISH POTATOES 



tive growth, grains usually responding best to phosphatic fertilizers, 

 while potatoes, in common with root crops, respond well to potash. 



In general, potato fertilizers are low in nitrogen and high in 

 phosphate and potash, the relative proportion usually being about 

 3810 for the different elements. This is a typical fertilizer exten- 

 sively used on the sandy soils of the Atlantic Coast, sandy soils being 

 very deficient in potash. It is generally believed now, however, that 

 the proportion of potash is higher than necessary. 



In the interior where potatoes are generally grown on heavier 

 soils and in rotation, the standard fertilizer, as above, is generally 

 used in smaller quantity, though experiments indicate that phosphate 

 is most important. Clay soils are usually well supplied with potash 

 which is made available by decaying organic matter. If clover is 

 grown in the rotation or farmyard manure is used for the potato crop, 

 there is not much need of adding nitrogen except to help early spring 

 growth. For such conditions, a fertilizer containing the elements 

 in the proportion of 3-10-6 will probably be about right. However, 

 experimenting is needed on each soil to determine the most profitable 

 fertilizer to use. 



Lime. Much of the land where potatoes are grown is quite 

 deficient in lime. On such soils lime will frequently give very 

 much increased yields. On the other hand, lime also makes favor- 

 able conditions for certain diseases of the tuber, especially potato 

 scab. Where potatoes are grown continuously, as on the Atlantic 

 Coast, the scab soon becomes so bad on limed soils as to cause great 

 injury. For this reason few of the growers are willing to use lime. 

 In fact, it is due to the acid soils of the Atlantic Coast that such 

 smooth, clean potatoes, free from disease, can be produced year after 

 year. 



Where potatoes are grown in rotation not oftener than once in 

 four years, there is not much danger from scab if clean seed is 

 planted. It is often necessary to use lime in order to grow clover 

 and grass and there is little danger of undue potato scab if the lime 

 is applied only once in four years and then at least two or three years 

 before the potato crop. 



Rotations. Where potatoes are grown as a regular farm crop, 

 it is customary to grow the potatoes after sod. No place is better 



