432 INVESTIGATION BY CULTURE EXPERIMENTS 



For this purpose these Pennsylvania data are probably the most 

 valuable the world affords; and, in the author's opinion, this 

 volume presents no more significant facts than are contained in 

 Table 81. 



The decrease in productive value of the unfertilized plot is 

 markedly uniform, notwithstanding the variation among those 

 plots, the average decrease in value per acre per annum being $2.87 

 and the widest variation from that average being 18 cents. Plot 8, 

 which had received manure during the 10 years previous to 1882, 

 shows the same decrease as the other four unfertilized plots, the 

 average for the four others being $i 1.46, while plot 8 shows $11.39. 

 The average yield of the No. 8 plots during the second 1 2-year 

 period is slightly less than the average yield of the four other 

 unfertilized plots during the first period. 



From Table 81, it will be seen that, for permanent systems of 

 farming, no form or combination of commercial plant food has been 

 used with profit, the annual loss from four acres varying from 

 $2. 46 with phosphorus alone, $3.59 with phosphorus and nitrogen, 

 and $5 (as an average) with phosphorus and potassium, to $20.40 

 and $32.70 with the complete fertilizer carrying the largest amounts 

 of dried blood and ammonium sulfate, respectively. 



Manure costing 30 cents a ton shows net profit in all cases, but 

 the profit is greatly reduced by the addition of caustic lime at 

 $4.50 a ton; although the lime produced sufficient increase to pay 

 $2.14 a ton for it for use with manure, and the effect of the lime- 

 manure treatment is distinctly cumulative, especially upon the 

 clover and timothy, the yield of hay from the lime-manure plots 

 being 640 pounds higher during the second 12 years than during 

 the earlier period, and 500 pounds more than from the manure 

 alone during the second period. 



Would ground limestone at less cost produce a greater benefit, 

 and would the use of phosphorus also with farm manure or green 

 manure produce still greater net profit? The Ohio investigations 

 answer the latter question with a most emphatic affirmative. 

 (See Tables 37, 38, 39, and 396.) 



Thus it will be noted that, as an average of the same 12 years 

 (1897 to 1908), the value of the produce per acre per annum is 

 1-35 where 12 tons of manure are used in the Pennsylvania 



