24 
Table VII. — Availability of iron and aluminum phosphates. 
Soil No. 2. 
Soil No. 3. 
Fertilizer added. 
"Weight of crop. 
Number 
of plants. 
Weight of crop. 
Number 
Green. 
Dry. 
Green. 
Dry. 
ofplants. 
N-K-Ca-L-P (ferrous phosphate) 
Grams. 
7.0 
0) • 
Grams. 
3.8 
1 
Grams. 
45.5 
41.0 
51.5 
55.0 
60.5 
88.5 
11.3 
70.0 
16.0 
29.5 
34.9 
Grams. 
. 21.5 
17.5 
35.5 
28.0 
31.8 
55.3 
5.3 
33.3 
9.5 
17.8 
20.0 
8 
N-K-Ca-P (ferrous phosphate > 
g 
N-K-L-P (ferrous phosphate) 
8 
42.5 
35.5 
18.6 
16.7 
8 
8 
8 
8 
8 
N-K-L-P (ferric phosphate) 
N-K-Ca-L-P (aluminum phosphate) 
N-K-Ca-P (aluminum phosphate) 
35.0 
35.5 
15.8 
16.7 
7 
7 
2 
8 
7 
N-K-Ca (check) 
8.5 
5.0 
4 
8 
N-K-L (check) 
8 
i No crop. 
In soil No. 2, ferrous phosphate apparently had a toxic influence 
upon the millet, while ferric and aluminum phosphate proved to be 
very available types of fertilizer. They were more readily available 
than phosphate rock, about equal to basic slag, but less readily assimi- 
lated than soluble phosphate. 
In case of soil No. 3, ferrous phosphate produced a good growth, 
due probably in part to the fact that this soil is more open and the 
ferrous salt may have been oxidized to ferric phosphate. Hence it 
may be said that both the iron salts and the aluminum salt are avail- 
able sources of phosphoric acid, more so in this type of soil than phos- 
phate rock, about the same as reverted phosphate and bone meal, 
but less than the other phosphates. 
In view of the action of lime upon the availability of the phosphates 
shown in the previous table (Experiment IV), pots were prepared to 
which the iron and aluminum phosphates were applied with and 
without lime. The results showed iron phosphates to be more avail- 
able without lime in this type of soil. The opposite relations held for 
aluminum phosphate. 
SAND CULTURES. 
A further test of the phosphates was made in sand culture to de- 
termine more precisely the action of the salts w T hen not under the in- 
fluence of complex soil conditions. Eighteen pots of silica sand were 
prepared, to each of which equal weights of nitrogen and potash fer- 
tilizer were applied in addition to the following, which *were run in 
duplicate: Ferrous, ferric, aluminum, sodium, titanium, and acid 
phosphates, phosphate rock, and slag. Two check pots received 
nitrogen and potash but no phosphoric acid. Each phosphate pot 
contained the same weight of phosphoric acid (P 2 5 ). 
