Circular No. 42 (Revision of No. 26). April, 19 14. 



WASSACHUSETTS AGRICULTURAL EXPERIMENT STATION. 



AMHERST. 



FERTILIZERS FOR POTATOES. 



WiM. P. Brooks, 



Fertilizers are in general regarded as superior to manures 

 Manures Com- for this crop. Principal reasons : 

 pared with 1. The period of growth is short; the plant food supply- 



Fertilizers, should therefore be in highly available forms. High grade 



fertilizers are superior to farm manures in this particular. 



2. The chances that the crop will be free from blight, rot and scab are 

 greater on fertilizers. 



3. Manures of good quality supply nitrogen in relatively large amounts, so 

 great that on the better soils the growth of vine is apt to be excessive on 

 manure. 



The above statements do not necessarily lead to the conclusion that manures 

 should never be used. They may give excellent crops, especially on the lighter 

 soils, deficient in humus and low in fertility ; but the quantity applied should 

 be moderate and applied broadcast, to be plowed or deeply harrowed in rather 

 than placed in hill or drill, and it will usually pay to use some fertilizer in 

 connection with the manure. 



Lime is alkaline in chemical character, and one of the most 

 Relation of Crop common and serious diseases from which potatoes suffer — 

 to Lime. ordinary scab, caused by the development of a fungus in 

 the surface tissues of the tuber — is favored by an alkaline con- 

 dition of the soil. 



An acid condition, while not protecting the crop in case of serious infection, 

 is not favorable to the scab fungus. The application of lime, then, in any con- 

 siderable quantity the same year that potatoes are planted is unwise. This 

 does not mean that soil on which potatoes are to be grown should never be limed. 

 Where the soil is inclined to be excessively acid and clover fails to do well, lime 

 may be used in moderation, but should be applied, if possible, some two or three 

 years before the land will be occupied by potatoes. 



Powdery scab, on the other hand, is apt to be more serious where soils are 

 acid ; and if this new disease gains a foothold and proves to be as difficult to 

 control as now seems likely, we may be forced to use lime in order to hold it in 

 check, as otherwise it may become more injurious than the ordinary scab. 



The first problem which will confront the potato grower is the 

 Selection of decision as to whether he will use one of the ready-mixed 

 Fertilizers. " Special " potato fertilizers, or, on the other hand, buy mater- 

 ials and make his own mixture. There are considerations 

 favorable to both plans. Some of the principal points favorable to the ready- 

 mixed fertilizers are : 



1. Some labor at a season apt to be crowded with work is saved. 



2. Such fertilizers are usually in good mechanical condition. 



3. In remote country places particularly they are easier to obtain. 



4. Selection may be somewhat easier, 'although it is not possible to buy under 

 the name " potato fertilizer " with certainty of obtaining the type of fertilizer 

 needed, for there is enormous variation between different so-called " potato fer- 

 tilizers." In our last fertilizer bulletin the analyses of ninety different brands 



