A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1177 



TABLE 20. 



RELATION OF DEPTH OF PLOWING TO YIELD ON 299 FARMS IN FRANKLIN 

 AND CLINTON COUNTIES IN 1913 \ 



planted was increased slightly as the depth of the plowing was increased, 

 the amount of fertilizer used was not increased. Consequently there would 

 be ample opportunity for any influence of depth of plowing to be reflected 

 in the yields under this method of study. The coefficient shown in figure 

 135 is 0.028 db 0.039, and indicates no relationship between the depth of 

 plowing and the yield. 



Yield per acre, in bushels 



III 

 r!? 



26 



14 



23 

 70 

 118 

 52 

 32 



;4 



299 



12 26 50 52 76 38 . 

 r = 0.028 0.039 



FlG. 135. CORRELATION OF DEPTH OF PLOWING AND YIELD ON 299 FRANKLIN AND 

 CLINTON COUNTY FARMS IN 1913 



MANURE AND FERTILIZER 



The commercial-fertilizer industry, as a country- wide enterprise, began 

 in the Eastern States and dates from about 1860. Previous to that time, 

 the potato crop depended for its plant food largely upon the natural 

 available supply of the soil, supplemented by applications of barnyard 

 manure. Manure has been recommended by many experiment stations 

 as perhaps the best source of nitrogenous plant food for this crop. How- 

 ever, as the acreage increased in the East and the soils became more 



