72 Report of the Department of Agronomy of the 



experiments it has given fully as good results as chemical equivalents 

 of freshly burned lime, hydrated lime, or air-slaked lime, any of 

 which is an impalpable powder. And it should not be overlooked 

 that the different forms have been compared in smaller quantities 

 than give maximum results on the soil in question. 



As to the limestone used in the Tennessee experiments it is stated 

 that " nineteen per ct. was too coarse to pass through a 20-mesh 

 sieve," which would make it about 10-mesh material. 



Rhode Island Bui. 145 reports experiments showing that ground 

 limestone was fully as effective as air-slaked lime, even for immediate 

 results. The fineness of the limestone is not given. 



Artificial (precipitated) calcium carbonate has been compared 

 with " Limestone meal " and the latter found to give fully as good 

 results, even for the first crop. (Experiment Station Record, 21:624.) 



In a comparison of crushed marble of different degrees of fineness 

 it has been found that material passing a one-millimeter (20-mesh) 

 sieve but coarser than a \ mm. (40-mesh) gave practically as good 

 results as that finer than \ mm., even for the first crop. (Rep't Penn. 

 State College, 1900.) 



When limestone is ground to pass a 10-mesh sieve from \ to § of 

 the product will pass a 40-mesh, depending somewhat upon the 

 nature of the stone and upon the kind of machinery used. The 

 entire product then is about as fine as representative samples of 

 " finely ground " bone meal, a mechanical analysis of which has 

 been found in our laboratory to be as follows: 



Fineness of Ground Bone Meal. 



Sample 3. 



Passing 10-mesh sieve 

 Passing 20-mesh sieve 

 Passing 40-mesh sieve 

 Passing 100-mesh sieve 



Per ct. 



94 

 71 



54 



28 



Fineness in bone meal is more important than in ground lime- 

 stone; for under soil conditions limestone (CaC0 3 ) is more soluble 

 than bone meal (Ca 3 (P04) 2 ), is used in quantities ten to twenty times 

 as great per acre, and costs about one-tenth as much per ton. Yet 

 bone meal of the above fineness is everywhere on the market and, 

 excepting for its cost, is a favorite form of phosphorus fertilizer. 



In humid regions limestone is leached out of the soil faster than 

 it is reduced by cropping. Evidence on this point is furnished by 

 the analyses of drainage waters reported from many sources. (See 

 Hilgard's Soils, p. 22; and Hall's Book of Rothamsted Experiments, 



