FORMS OF LIME AND CROP VALUE 353 



sition of their products, it is well to know the quality 

 of the material before purchasing it. The carbonate of 

 lime in marl may vary from 5 or 10 to 90 or 95 per cent 

 in different samples. 



Ground limestone has been used as a substitute for 

 marl. It is very important that it be finely ground, as 

 upon the comminution of the material much of its effi- 

 ciency depends. As there was some question as to the 

 value of ground limestone, experiments in which it was 

 compared with caustic lime have been conducted at 

 some of the experiment stations. These have, in the 

 main, given results very favorable to finely ground lime- 

 stone. 



Frear reports tests in which plats treated with slaked 

 lime, at the rate of two tons per acre once in four years, 

 were compared with plats treated with ground limestone, 

 at the rate of two tons per acre every two years. The 

 records, at the end of twenty years, show that in every 

 case the total yields were greater on the plats receiving 

 ground limestone. After the treatment on these plats 

 had been continued for sixteen years, a determination of 

 nitrogen showed the upper nine inches of soil on the 

 limestone-treated plats to contain 2,979 pounds of nitro- 

 gen per acre, and the siaked-lime plats to contain 2,604 

 pounds. It may be inferred from these figures that the 

 slaked lime caused a greater destruction of organic 

 matter than did the limestone. 



Patterson also conducted experiments for eleven 

 years with caustic lime produced by burning both stone 

 and shells, and the carbonate of lime in ground shells 

 and shell marl. The average crops of maize, wheat 



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