426 INVESTIGATION BY CULTURE EXPERIMENTS 



).75, as an average of the 24 years. With 16 tons the increase 

 was $21.07, an d with 20 tons it was $22.73. Thus, the 12 tons were 

 worth $1.65 a ton, 16 tons were worth $1.32 a ton, and 20 tons were 

 worth $1.14 a ton. Thus, we may say that the first 12 tons were 

 worth $1.65 a ton, the next 4 tons were worth 33 cents each, and 

 the last 4 tons were worth 42 cents each, or, as an average, the 8 

 tons of manure applied after the first 12 tons were worth 37 cents 

 a ton. 



The " cost of treatment " for the manure applied may be de- 

 termined in at least three different ways: 



First, we may consider the manure as a by-product of the farm 

 and only allow for the cost of hauling and spreading, for which 30 

 cents a ton is sufficient, as a rule. This is the figure used in the 

 tables under discussion. 



Second, we may estimate the cost of shipping manure from some 

 fairly large source of supply, such as the stock yards of Chicago 

 or other cities. This cost would probably amount to $i to $2 

 per ton, including the hauling from the railway station and spread- 

 ing on the land. 



Third, we may purchase feed and thus produce manure on the 

 farm and allow for the manure whatever is necessary! 



Table 78 shows the average value of the manure applied at differ- 

 ent rates, and also the profit from using the manure that is regularly 

 produced on the farm. 



There is no record of the amounts of manure applied to plot 8 

 (on the four series) previous to the beginning of these experiments; 

 but its residual effect is very apparent, the average increase 

 amounting to $3.23 per acre per annum for the 24-year period, in 

 comparison with the unfertilized plots. 



Caustic lime alone decreased the crop yields as an average, but 

 when used with manure it produced an average increase of $2.49, 

 or about 25 per cent of its cost at $4.50 per ton. As an average 

 of the two tests, the light application of land-plaster produced 

 practically no effect. The heavy applications of ground limestone 

 produce an average increase of $2.71, or not quite half its cost at 

 $1.50 per ton. In the last four or five years the effect of ground 

 limestone alone is apparently decreasing, a result to be expected 

 sooner or later where no manure or plant food is returned to the 



