546 VARIOUS FERTILITY FACTORS 



tons of manure, applied at the annual rate of 15.7 tons per acre for 

 six years (1876 to 1881), produced 1326 bushels' increase in the 

 potatoes during the 26 years (1876 to 1901), which at 50 cents a 

 bushel would give the manure a value of $7.04 per ton. Here the 

 plant food applied in the 94.2 tons of manure was from two to four 

 times that removed from the soil in the 1326 bushels' increase in 

 potatoes, and the subsequent yields of barley show that the manure 

 still produces some residual effect. However, the large amount 

 applied during the six years is equivalent to 3 tons of manure per 

 acre per annum for more than 30 years. 



When measured by crop yields, the value of a ton of manure 

 increases with the size of the area over which it is spread, but the 

 yield and profit per acre usually increases with the amount of 

 manure applied. Hence, with much land and little manure, light 

 applications are most profitable; while with less land and much 

 manure available, heavy applications bring the greatest profit. 

 It should be remembered, too, that manure may act as a power- 

 ful soil stimulant, when light, infrequent applications are made on 

 good land, from which more plant food is removed in crops than is 

 applied in the manure. 



In an experiment conducted at Cornell University, 4000 pounds 

 of ordinary manure from the horse stable, worth $2.74 per ton for 

 the plant food content (at commercial prices) were exposed in a 

 pile out of doors from April 25 to September 22, but at the end of 

 that time the total weight had decreased to 1 770 pounds, worth only 

 $2.34 per ton. In other words, the value of this pile of manure was 

 reduced from $5.48 to $2.03 during five months' exposure. In 

 another Cornell experiment, manure exposed for six months lost 

 56 per cent of its dry matter and 43 per cent of its plant-food value. 

 In this case the fresh manure was worth $2.27 a ton, while the 

 rotted manure was worth $3.01 a ton (at commercial prices for 

 plant food), but the total loss in weight and plant food was such 

 that for each ton originally worth $2.27 there remained only $1.30 

 worth after six months' exposure. 



The Ohio Agricultural Experiment Station placed five lots of 

 manure, of 1000 pounds each, in flat piles in the barnyard. Four 

 of these lots of manure had been treated with materials, as indicated 

 in Table 112, at the rate of 40 pounds per ton of manure. The 



