USE OF PHOSPHORUS IN DIFFERENT FORMS 261 



nary high-grade raw phosphate carries very little, if any, lime, 

 about 7 per cent of calcium carbonate being the largest amount 

 in any high-grade phosphate known to the author. Tricalcium 

 phosphate is a neutral substance which has practically no power 

 to correct soil acidity, except as the phosphorus is converted into 

 the dicalcium or monocalcium compound and removed from the 

 soil by the growing crop. 



Furthermore, the most marked benefit from the use of raw rock 

 phosphate in Illinois is not on markedly acid soils, but on the 

 most common corn-belt prairie land, as on the Urbana and Gales- 

 burg experiment fields on brown silt loams, which are practically 

 neutral soils valued at $150 to $200 an acre. 



The Ohio investigations with raw and acid phosphates are in a 

 class by themselves. No others have been conducted anywhere 

 in the world that can compare with these in agricultural value. 

 Many experiments with various phosphates have been carried on 

 for a single season, and some for several years, but, as a rule, no 

 farm manure has been used, and no adequate provision made for a 

 supply of decaying organic matter. Where nitrogen has been sup- 

 plied, it has usually been in some commercial form, such as sodium 

 nitrate. One exception to this is found in the Maryland experi- 

 ments, which have been conducted on one field since 1895, eleven 

 years' results having been reported by Director Patterson (Mary- 

 land Bulletin 114). Aside from single plots treated with different 

 acid phosphates and reverted phosphates in the Crimson Clover 

 Series, there is a strictly comparable triplicate test with (i) raw 

 bone meal, (2) slag phosphate, (3) no phosphate, (4) South Caro- 

 lina raw rock phosphate, and (5) Florida soft rock phosphate 

 (containing phosphates of iron and aluminum). Equal amounts 

 of phosphorus were used in all tests, 65^ pounds of phosphorus 

 per acre having been applied only at the beginning of the experi- 

 ment. The surface soil contained 1300 pounds of phosphorus 

 in 2 million pounds of the soil. 



The following crops were grown: 



Corn in 1895. Wheat in 1899. Corn in 1903. 



Corn in 1896. Hay in 1900. Wheat in 1904. 



Corn in 1897. Hay in 1901. Hay in 1905. 



Crop failure in 1898. Corn in 1902. Corn in 1906. 



