In deciding what materials to use for making the potato fer- 



The Sources of tilizer the principal points to be considered are cost and 



the Different suitability for the crop. It is not ^possible to give formulas 



Plant-food Ele- which shall be permanently best. Relative prices of sources 



ments. respectively of nitrogen, phosphoric acid and potash vary from 



year to year, and even in some cases from month to month. 



The end to be aimed at is, of course, the same in the case of all plant-food 



elements, viz. : to obtain the greatest possible number of pounds of available 



plant-food for the. money expended. The ton price is no indication as to whether 



a fertilizer is dear or cheap. Fertilizers of the highest ton price are sometimes 



the cheapest. 



In order to make it safe to apply the entire amount of fertil- 

 The Nitrogen izer needed for the crop at planting time the nitrogen should 

 Supply. be derived from materials possessing a varying rate of avail- 



ability, such, for example, as nitrate of soda, sulfate of am- 

 monia, cyanamid, dried blood and tankage. 



Nitrate of soda is immediately available. Sulfate of ammonia, cyanamid and 

 dried blood require a little time and are about equally available. Tankage is 

 slower in its action. The proportion of cyanamid must be small, for otherwise 

 there may be loss of ammonia from organic materials or sulfate of ammonia if 

 these constitute a part of the mixture. Such loss, however, is not probable if the 

 mixture contains also a considerable proportion of acid phosphate, for this will 

 be likely to combine with the excess of lime in the cyanamid. As a conse- 

 quence of such combination the phosphoric acid of the acid phosphate may be 

 somewhat decreased in solubility, but it will still be available. 



Other materials which may be considered as sources of nitrogen are dry-ground 

 fish, cottonseed meal and bone meal, but the first is usually high in price and 

 the others are not as a rule as suitable or available as the materials named. 



There is no doubt that the presence of a liberal amount of 

 Phosphoric Acid, phosphoric acid in a fertilizer for potatoes is favorable to 

 early maturity, and wherever an early crop is important or 

 where there is a tendency to excessive growth of vine, this element in soluble 

 form should be relatively abundant in the fertilizer. Acid phosphate should be 

 mainly depended upon, but a small proportion of the phosphoric acid in the 

 form of tankage, fish or bone is not undesirable. Basic slag meal is absolutely 

 unsuitable for potatoes on account of the excess of lime it contains. 



The potash of a potato fertilizer should, I believe, usually 

 Potash. be supplied in the form of sulfate rather than muriate, al- 



though on light soils, especially those rich in lime, and in ex- 

 cessively dry seasons the muriate may be preferable. On the soils of the col- 

 lege farm wherever these two salts have been compared the sulfate has generally 

 given a slightly heavier crop, and the quality, as indicated by the percentage of 

 starch, and mealiness and flavor when cooked, has been superior. 



A very large number of comparisons between these two salts has been made. 

 The average of the trials on the different fields has in all cases been a larger 

 yield on the sulfate, the difference in its favor ranging from one bushel per acre 

 in one case to 53 bushels in another. The average of the 51 different com- 

 parisons between these two salts for potatoes shows for the muriate a yield of 

 207.4 bushels per acre; for the high grade sulfate, 218.6 bushels. The average 

 difference, therefore, in favor of the sulfate is 11.2 bushels, a quantity which is 

 much more than sufficient to . cover the difference in cost between the two salts. 

 The quality of the tubers on the sulfate, moreover, is superior. The differ- 

 ence is indicated by the following figures, which represent the average of three 

 experiments: Potatoes raised on sulfate of potash, water 78.11%; on muriate, 

 79.86'I(i. Per cent, of starch in potatoes raised on sulfate, 14.99%; on muriate, 

 13.68%. 



Wood ashes are not a good source of potash for potatoes on account of their 

 alkaline character. 



