1178 EARLE V. HARDENBURG 



impoverished, the need for a commercial source of plant food became 

 imperative. Today there are few crops which require more and respond 

 be'tter to fertilizer than do potatoes, tho even yet commercial fertilizer 

 is used very little on the newer potato lands of Michigan, Wisconsin, and 

 Minnesota. From the beginning of the fertilizer industry, hundreds of 

 tests have been conducted by the eastern state experiment stations to 

 determine the influence on the yield of potatoes of such factors as the 

 amount of fertilizer used, its analysis, and the time and method of its 

 application. According to Whitney (1910) v 1769 such tests were conducted 

 between 1868 and 1908, a period of forty years. Of all the tests made 

 up to 1908, nearly 72 per cent fall within the ten-years period from 1890 to 

 1900. Twenty-three States contributed to these tests, and about 57 per 

 cent of the total were made in New York, Ohio, and New Jersey. Whitney 

 states that it is impossible to draw conclusions even from an average of simi- 

 lar experiments among those listed, since the variation in the yields of check 

 plots of individual experiments sometimes ranges as high as 900 per cent. 

 The crop survey has been found to have its limitations in the study of 

 such questions as best analysis, best amount, or best source of ingredients, 

 of a fertilizer to be used for potatoes. It is generally impossible to get 

 information from the grower as to the analysis or the source of the elements 

 of the fertilizer he has used. Many growers who were .questioned had 

 been more impressed by the brand name or by the price paid for the 

 fertilizer than by its analysis. An attempt to correlate the amount of 

 fertilizer per acre with the yield resulting was found impracticable with- 

 out knowledge of its analysis, owing to the fact that large applications of 

 a cheap fertilizer might be no more than equivalent to small applications 

 of a high-grade fertilizer. Furthermore, many growers used manure 

 in place of fertilizer, or vice versa, while many others used both on the 

 same acreage. The study of the influence of manure and fertilizer on 

 yield in the surveyed regions has therefore been made on the basis of the 

 combined value per acre of manure and fertilizer. Estimates of the value 

 of the manure used, made by the grower, and the prices he paid for fertilizer, 

 have been used. In determining the proportion of the total value of the 

 manure received by the potato crop, depending on the time and place of 

 its application, 50 per cent of its value was charged if it was applied directly 

 to the potato crop, 30 per cent if it was applied to the crop just preceding 

 the potatoes, and 20 per cent if it had been applied two years before 

 potatoes. This evaluation of residual manure is not based on exact 

 experimental knowledge, but is presumed to represent the approximate 

 availability of stable manure for successive crops. The Department 

 of Agricultural Economics and Farm Management at Cornell University 

 estimates that, on the heavier soils, 40, 30, 20, and 10 per cent of the 

 value of manure is received by the first, the second, the third, and the 

 fourth crop after its application, respectively. On lighter soils, which 



