PHOSPHORUS FOR SOILS. 183 



them acid. Indeed it is even asserted that soils containing an 

 abundance of lime in the beginning may be made acid by the 

 continued use of superphosphate if no lime is added. 



When the natural phosphates alone are considered there is no 

 doubt that the preference should be given to those derived from 

 bones. The organic matter present in the bones decays when it is 

 incorporated with the soil, and this process doubtless causes the 

 phosphate to become more readily available to the plant, while 

 the rock phosphate on the contrary is very slowly decomposed. 

 The degree of fineness to which bone meal or mineral phosphate 

 is ground is of prime importance. Very fine bone meal is much 

 more available than that which is coarser and is always rated at 

 a higher price a ton. 



Vsinff Floats with Manure. — The use of fioats, or finely ground 

 phosphate rock, has not met with general favor, and it probably 

 does not give good results when used alone. Some of the earlier 

 experiments indicate that it has practically no value as a source 

 of phosphoric acid for the plant. Recent investigations at the 

 Ohio and Illinois Experiment Stations show that when floats are 

 added to farm manure it has a very high fertilizing value; in 

 fact the increased crop production in Ohio due to adding the 

 ground rock phosphate to the stall manure was nearly as large 

 as that obtained from the addition of superphosphate. The acid 

 substances produced during the decay of the manure apparently 

 make the phosphoric acid in the rock more available, and it 

 would seem from these experiments that the comparatively in- 

 expensive floats might, partially at least, replace superphosphate 

 if used in connection with the manure. Other experiments have 

 demonstrated that good results can be obtained from the use of 

 ground rock phosphate when plowed under with a green manure 

 crop like clover, but that it is of very little value if used on a 

 soil low in organic matter. In a plot experiment at the Mass- 

 achusetts experiment station two "equal money's worth" of 

 ground Carolina rock and superphosphates were compared. In 

 this case the superphosphate proved superior at first, but within 

 a few years the plot to which rock phosphate was added gave 

 higher yields. It would seem, on the whole, that Jhe use of 

 floats with manure is worthy of a trial by anyone needing a 

 phosphate fertilizer. Ohio Bulletin 134 recommends that the 

 ground rock be used "as an absorbent in the stable, thus secur- 

 ing an intimate mixture with the manure in its fresh condition." 



Raw Phosphatic RocJc for Alfalfa. — Eaw rock, 

 or floats, the natural Tennessee, South Carolina 



