1 66 SYSTEMS OF PERMANENT AGRICULTURE 



" In each case the yields with the carbonate of lime showed superiority under 

 the conditions of this experiment over those following an equivalent application 

 of caustic lime. " 



After these experiments had been in progress for sixteen years, 

 the soil of each of the four plots in each test was sampled for analy- 

 sis. The average nitrogen content for the four plots receiving 

 ground limestone was found to be 2979 pounds per acre to a depth 

 of 9 inches, while only 2604 pounds were found in the soil treated 

 with caustic lime. This difference of 375 pounds of nitrogen is 

 equal to the nitrogen contained in 37^ tons of farm manure. In 

 other words, the data indicate that the effect of caustic lime as 

 compared with ground limestone was equivalent to the destruction 

 of 37^ tons of farm manure in 16 years, or more than two tons a 

 year to the acre. Or, if we count the soil nitrogen worth 15 cents a 

 pound (a fair market price), there is a liberation of more than 

 $7.00 worth of nitrogen for every ton of burned lime used during 

 the 1 6 years. 



The estimation of humus in these soils, based upon the determi- 

 nation of organic carbon (multiplied by Wolff's factor, 1.724), 

 showed the soil receiving limestone to contain 37.9 tons of humus 

 per acre to a depth of 9 inches (counting 300,000 pounds of soil to 

 the acre-inch), while only 34.2 tons of humus remained in the soil 

 treated with caustic lime. If 4 tons of farm manure contain only 

 i ton of dry matter (average fresh farm manure contains about 

 75 per cent of water), and if 2 tons of dry matter would be re- 

 quired to make i ton of humus (when exposed to the weather, 

 manure usually loses half of its dry-matter content within one 

 year or less), then this difference of 4.7 tons of humus would be 

 equal to 37.6 tons of fresh farm manure, which represents the loss 

 from the destructive action of caustic lime as compared with 

 ground limestone. 



During the 20 years, the land treated with ground limestone 

 produced per acre 99 bushels more corn, 116 bushels more oats, 

 13 bushels more wheat, and 5.6 tons more hay, than the land treated 

 with caustic lime. Counting 35 cents a bushel for corn, 30 cents 

 for oats, 70 cents for wheat, and $6.00 a ton for hay, the value of 

 the produce from the limestone treatment was $112.15 more than 

 that from the land treated with caustic lime. The total ultimate 



