488 Journal of Agricultural Research voi. vi, no. 13 



phate than on calcium phosphate, and "six made better growth on iron 

 phosphate than on calcium phosphate." 



Under the direction of Hopkins (8), the Illinois Experiment Station is 

 conducting probably the most extensive investigation of any in the 

 world on the use of rock phosphate. Some of the most interesting 

 results were obtained from a field near Galesburg, Knox County, 111., on 

 brown silt loam prairie soil. 



Phosphorus applied in fine-ground natural rock phosphate in part as top dressing, 

 and with no adequate provision for decaying organic matter, paid only 47 per cent on 

 the investment as an average of the first three years. But it should be kept in mind 

 that the word investment is here used in its proper sense, for the phosphorus that was 

 removed in the increase produced was less than 2 per cent of the amoim.t applied, 

 and that removed in the total crops less than one-third. During the last six years, 

 however, the phosphorus has paid 130 per cent on the investment, even though two- 

 thirds of the application remains to positively enrich the soil (8, p. 15). 



Newman (16) investigated the use of floats with and without cotton- 

 seed meal. He found a marked increase in availability where organic 

 matter was used in conjunction with the mineral phosphate. Later 

 experiments by Newman and Clayton (17) confirmed the above results. 

 Lupton (13) continued the work of Newman, but used acid phosphate as 

 a check on the raw rock phosphate, both with and without organic matter. 

 His results are also in accord with Newman's earlier experiments. Where 

 floats were mixed with cottonseed meal and allowed to ferment, the data 

 seemed to show that the fermentation of the material had very little, if 

 any, influence on the availability of the phosphate. Pfeiffer and Thur- 

 man (19) found no beneficial results from composting raw rock phosphate 

 with decaying organic matter. In Canada (23) fermenting manures 

 were found to have only slightly solvent action on composted rock 

 phosphate. 



Hartwell and Pember (6) mixed fresh cow manure and floats and 

 allowed them to ferment. They feel that there was practically no 

 increase in the availability of phosphorus in the floats. McDowell (14) 

 also found no increase in the availability of phosphate in finely ground 

 rock phosphate by composting the mineral with cow and horse manure. 

 Tottingham and Hoffmann (26), following the same line of investigation 

 as that which McDowell observed, actually found a decrease in water- 

 soluble phosphorus, but the results were similar with acid phosphate. 



Krober (12) was unable to find any increase in availability of mineral 

 phosphates by composting with sawdust and allowing fermentation to 

 proceed. Truog (27) believes that fermented manure has a slightly 

 solvent action on crude phosphate. He also points out that a uniform 

 distribution of the phosphate in the soil will give much better results 

 than that poorly distributed. 



Krober (12) shows that the acid-forming bacteria and yeasts are of 

 great value in rendering some of the phosphorus in insoluble phosphate 



