Active Phosphoric Acid and Pot Experiments. 
49 
9-10 ......... 1 5 2 13 63 24 
11-19 ......... 1 5 5 9 45 46 
32-42 ......... 2 . . 4 33 .. 66 
Total ........ 48 47 16 
The percentage of non-deficient soils increases with fair regularity 
throughout the table, though there are some breaks, notably in group 
7-8, all soils in which are deficient. 
In groups 3 to 10 are fifty soils, twelve of which are very de- 
ficient, 37 are deficient, and six appear to yield sufficient phosphoric 
acid. That is to say, about eleven per cent are not deficient. The 
average corn crop without phosphoric acid is from 34 to 71 per 
cent of that with phosphoric acid. We feel justified in drawing the 
following conclusions. 
Soils containing from 30 to 100 parts per million of phosphoric 
acid soluble in N-5 nitric acid, are, as a rule, deficient in phosphoric 
acid, and the extent of their deficiency is related to the quantity of 
active phosphoric acid. 
Group 11-19 contains only eleven soils. Nearly fifty per cent are 
not deficient. We draw the following conclusions, subject to modifi- 
cation when a larger number of soils are studied: 
Soils containing from 100 to 200 parts per million of active phos- 
phoric acid are possibly deficient in phosphoric acid, the chances 
being even that they are, or are not. 
Group 32-42 contains only six soils. Such soils are likely not to 
be deficient in phosphoric acid, but this conclusion is likewise sub- 
ject to modification from further study. 
SUMMARY AND CONCLUSIONS. 
The active phosphoric acid of the soil appears to be related to the 
needs of the soil as shown by pot experiments. A number of fac- 
tors must be taken into consideration in applying these results. 
