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. 
Using Floats with Manure.—The use of floats, 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 the 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 Rock for Alfalfa—Raw rock, 
or floats, the natural Tennessee, South Carolina 
