80 Bureau of Farmers' Institutes. 



humus — vegetable matter — in the soil. As a rule, there is pot- 

 ash enough in the soil, and, if there is a good clover sod, nitrogen 

 enough to grow a potato crop. If you want to add a commercial 

 fertilizer, apply South Carolina rock. 



Question. — What is the cause of potato scab? Is it a potato 

 disease or a soil condition? What is the cure? 



Mr. Ivice. — It is a parasitic disease. It prefers an alkaline soil, 

 one that has lime in it. If the soil is acid, the disease will quickly 

 die out. I know of no absolute way by which the scab can be 

 entirely eradicated in a soil where it has become really established. 

 Sulphur is used in the potato hills. We also soak the seed in a 

 solution of two ounces of corrosive sublimate dissolved in two 

 gallons of water, one hour; take them out, allow them to dry, then 

 cut for seed. This will eradicate all the scab, if there is any on 

 the potatoes. I have never used the formaline treatment, al- 

 though it is recommended by the experiment stations. It is prefer- 

 able, however, to change the field for potatoes every year, to 

 avoid scab getting into the soil, which soaking the potato does not 

 eradicate. 



Question. — What is your opinion of potatoes for seed that were 

 blighted the previous year ? 



Mr. Fenner. — I should not care to plant potatoes that had been 

 blighted, but if I did, I should select the best specimens — those 

 most nearly typical of the variety. 



Question. — What is the best commercial fertilizer for potatoes, 

 and which is the best way to apply it? 



Mr. Smith.'— I don't know. It will all depend on the soil and 

 cultivation. We can only give you some underlying principles 

 to be governed by. One must watch the plant. Too much nitro- 

 gen will produce an overgrowth of stalk or straw. Potash will 

 add strength to stalk and vine and color to fruit and foliage, while 

 phosphoric acid perfects seed. As a rule, there is potash and 

 nitrogen enough in the soil. What is most lacking is phosphoric 

 acid. That must be present in sufficient quantity and be available 

 for the use of the plant. By available is meant solubility in soil 

 water. Unless there is present soil water, plant food is not avail- 

 able. Then, too, unless the South Carolina rock has been treated 

 with sulphuric acid, it will not be available. I do not know how 

 much acid is needed to reduce the crude rock, but it is a consider- 

 able quantity. On Long Island a formula is used consisting of 

 4 per cent, of nitrogen, 8 of potash and 10 of phosphoric acid. 

 In commercial fertilizers, 1,000 pounds per acre, sometimes 



