OHIO FIELD EXPERIMENTS 449 



given in the last column of Table 83 are based upon the price of 

 50 cents a bushel for potatoes, while 30 cents a bushel is the price 

 used in the other computations. Of course the increase in crop 

 values resulting from treatment is not computed at the delivered 

 price for marketable potatoes, but sometimes this would be justi- 

 fied, because the treatment may largely increase the percentage of 

 marketable potatoes, and even with other crops the improvement 

 in quality, as well as in quantity, may be a factor of some impor- 

 tance. In any case, potatoes belong to the crops of intensive agri- 

 culture, the largest average yield (200 bushels) amounting to $60 

 an acre at 30 cents, and to $100 an acre at 50 cents a bushel. 



Part of the field upon which these experiments have been con- 

 ducted was virgin soil, cleared from forest for the purpose, and all 

 of the land was fairly rich at the beginning. 



The average of 16 analyses of soil from the " East Farm," where 

 the five-year rotation (Table 82) and reenforced manure experi- 

 ments (Table 40) are conducted, and 5 analyses of soil from the 

 " South Farm," where the potato- wheat-clover rotation experi- 

 ments are under way, show that the South Farm soil contains about 

 one half more acid-soluble phosphorus than the East Farm soil. 

 It is also somewhat richer in acid-soluble potassium, while in 

 total nitrogen the East Farm soil is slightly richer. By referring 

 to the column headed " Value if unfertilized " (Table 83), it will 

 be seen that the natural productiveness of the land varies markedly 

 from plot i ($83.70) to plot 19 ($68.03) and plot 34 ($63.40); 

 but the oft-repeated check plot (unfertilized) makes possible a 

 comparison that could not be made without it. On the other hand, 

 we can never be sure that the treatment applied to one plot (as 

 phosphorus to plot 2, for example) has produced the same total 

 increase as it would have produced if applied to some other plot 

 (as to plot 20, for example) . Thus the actual total yield from plot 2 

 ($92.65) is greater than that from plot 20 ($90.85), but the computed 

 increase from plot 20 is more than twice as great ($22.21) as that 

 from plot 2 ($9.36). The fact is that more plant food is removed 

 from plot 2 than from plot 20, but this is also true, of course, with 

 respect to the adjoining unfertilized control plots. These difficul- 

 ties are emphasized, however, by comparing plots n and 20, both 

 of which receive the three elements, nitrogen, phosphorus, and po- 



