LIMESTONE 



167 



effect of the caustic lime for the 20 years was an actual decrease 

 in the yields of all crops except wheat; while the ground limestone 

 produced an increase in all crops except corn, on which the de- 

 crease was only one sixth as much as with caustic lime. 



If it is true, as indicated by the Pennsylvania experiments, 

 that 8 tons of burned lime, applied during 16 years, released 375 

 pounds of nitrogen and destroyed organic matter equivalent to 

 37 tons of farm manure, or more than $7.00 worth of nitrogen and 

 4| tons of manure destroyed for each ton of burned lime used, as 

 compared with ground limestone ; and if larger crops were obtained 

 where limestone was used, especially where the practice is extended 

 over several years, and if the ground limestone is sustaining the 

 productive capacity of the soil much better than the burned lime ; 

 then, as a very general rule, we should avoid applying caustic 

 lime to the land, but make liberal use of ground limestone where 

 needed to correct the acidity of the soil and to furnish a natural 

 base, although, as used in these Pennsylvania experiments, without 

 manure and with no return of plant food, the increase in crop 

 yields produced by ground limestone has not been sufficient to 

 pay for the heavy applications. 



The Maryland Experiment Station has recently reported experi- 

 ments with different kinds of lime, covering eleven years, with a 

 rotation of corn, wheat, and hay (timothy and clover), 1400 pounds 

 of calcium oxid (burned lime) and equivalent amounts of calcium 

 carbonate (ground oyster shells and shell marl) having been applied 

 per acre at the beginning. Four crops of corn, three of wheat, and 

 four of hay were harvested during the eleven years, with the follow- 

 ing total results per acre: 



TABLE 25.1. MARYLAND EXPERIMENTS WITH LIME 



1 Average of two plots. 



