2 66 SYSTEMS OF PERMANENT AGRICULTURE 



The soil of the farm of the Pennsylvania State College is a resid- 

 ual clay loam from the disintegration, weathering, and leaching of 

 impure limestone. The soil contains 85 to 90 per cent of fine earth 

 and 10 to 15 per cent of small stones, quartz, silicates, etc. In 

 2 million pounds of the fine earth of this surface soil there are 1090 

 pounds of acid-soluble phosphorus and 50,700 pounds of total 

 potassium, an amount equivalent to $3000 worth of commercial 

 potassium salts. 



The following comments concerning these experiments are made 

 by the Pennsylvania Station (Annual Report for 1895, page 210), 

 on the basis of prices prevailing at that time: 



"The yearly average for the twelve years gives us a gain per year of $2.83 

 from insoluble phosphorus l (ground bone), $2.45 from insoluble phosphorus 

 (South Carolina rock), $1.61 from reverted phosphorus, and 48 cents from 

 soluble phosphorus, thus giving us considerably better results from the two 

 forms of insoluble phosphorus than from the reverted or soluble forms, thus 

 indicating that the insoluble phosphorus is of more value as a manure than is 

 often supposed, and that it is worthy of more attention -than has been given to 

 it in the past." 



In 1894, the Rhode Island Experiment Station began an inves- 

 tigation to ascertain the relative value of eight different forms of 

 phosphorus, and a ninth form (double superphosphate) was intro- 

 duced in 1895. The experiment included the common raw rock 

 phosphate (containing tricalcium phosphate), raw and roasted 

 aluminum phosphate (containing also some iron phosphate), 

 basic slag phosphate, steamed bone meal, and three acid phos- 

 phates (one made from raw rock, one from bone meal, and one 

 from bone black), besides the double superphosphate. The fol- 

 lowing statements from Rhode Island Bulletin 114 give further 

 information : 



"According to the original plan of Ex-Director Flagg, like money values of 

 phosphate were to be compared, and the applications were made for several 

 years upon that basis. Owing, however, to the widely varying market prices 

 from year to year, it was decided in 1898 to change the plan of the experiment 

 so as to make it a comparison of like amounts of phosphorus. 2 



1 Substituted for " phosphoric acid" here and elsewhere. 



2 Substituted for "phosphoric acid" here and elsewhere, with equivalent amounts. 



