No. 4.] MODERM POTATO CULTURE. 49 



England are extremely variable in character and composi- 

 tion, and it is therefore Impracticable to make a fertilizer 

 formula for potatoes or any other crop that would be appli- 

 cable in all eases. Each fanner who uses commercial ferti- 

 lizers extensively should experiment with unmixed goods 

 enough to determine to what elements his soil most readily 

 and profitably responds. Some marl or limestone soils are 

 quite rich in phosphoric acid, and consequently a fertilizer 

 containing a small amount of that element and relatively larjje 

 amounts of nitrogen and potash would give best results, 

 while some of our granite soils and clay loams are quite rich 

 in potash, and respond best to a fertilizer containing rela- 

 tively large amounts of phosphoric acid. 



A stud} r of the experimental data indicates that the potato 

 plant thrives best in a rich soil which is abundantly supplied 

 with all fertilizing elements. In the early stages of its 

 growth, when the vines are forming, the demand for nitro- 

 gen is particularly large, and for this reason a potato ferti- 

 lizer should contain quite a part of its nitrogen in a soluble, 

 immediately available form. Later in the season, when the 

 tubers are forming, large amounts of phosphoric acid and 

 potash are required, also a bountiful supply of water to take 

 up the plant food and transmit it through the vines. 



The Water Supply . 



There is no farm crop that is more easily, speedily and 

 greatly affected by the supply of moisture than is the potato. 

 It has been found by experiment that it takes about 425 

 tons of water to grow a ton of dry matter of potatoes. A 

 crop of 200 bushels per acre would therefore require approxi- 

 mately G50 tons of water, equivalent to a rainfall of nearly 

 six inches. Because of its need for large water supply, and 

 its remarkable susceptibility to climatic conditions, it follows 

 that the average potato yield is affected more by water 

 supply than by lack of plant food. The selection of soil 

 and methods of culture must be with this fact in view if 

 success is to be had. The liberal application of fertilizers 

 or the presence of large amounts of readily available plant 

 food will prove of but little value if the moisture supply is 



