42 
Efficiency of the phosphoric acid as ajjected by the stage of growth of 
the crop. — An attempt was made to determine whether the guanos 
were equally efficient phosphatic fertilizers at all stages of the plant's 
growth. It might be thought that the more unavailable phosphates 
would be more efficient during the later stages of plant growth, when 
the root system is more developed, than during early growth. 
The efficiencies of bone meal and seven guanos were tested relative 
to acid phosphate with millet grown 31, 41, and 51 days, or with corn 
grown 39 and 55 days. Kiver sand No. 213 with a water content of 
18 per cent was used, 46 pounds dry soil per pot for the corn, 47 for 
the millet crops. The corn was grown from February 2 to March 29, 
1915, the millet from July 4 to August 24, 1915. At 31 days the heads 
of millet were just appearing, at 41 da\s seeds were forming but were 
not fully ripe, and at 51 days the seeds were ripe and the plant com- 
mencing to dry. The corn commenced to show pronounced joints at 
39 days (after transplanting seedlings to pots) and at 55 days tassels 
were out on many plants. In order that plants grown 55 days might 
not be restricted in growth by the size of the pot more than those 
grown 39 days, four seedlings to a pot were planted in the 39-day 
series and 2 seedlings to a pot in the 55-day series, while 29 millet 
plants were grown per pot for all three tests. Results of the tests 
are given in Table XVIII. 
Table XVIII. — Effect of period of growth of crop on the immediate availability of the 
phosphoric acid in guanos. 
CORN GROWN 39 DAYS. 
Phos- 
phoric 
Source of phos- 
acid 
phoric acid 
ap- 
(P2O5). 
plied 
per 
pot. 
Gm. 
No phosphate 
Acid phosphate 
0.30 
Do 
.60 
.90 
1.35 
Do 
Do 
Do 
2.03 
Guano No. 500 
2.40 
Guano No. 503 
1.40 
Guano No. 504 
10.00 
Guano No. 507 
3.00 
Basic fertilizer 
applied per pot. 
Oven -dry yield of individual 
pots. 
Average 
oven-dry 
yield and 
probable 
error. 
Efficiency 
of phos- 
phoric acid 
as com- 
pared with 
that of 
acid phos- 
phate =100. 
Sodium nitrate, 
8.4 gm.; am- 
monium chlorid, 
5.3 gm. ; potas- 
sium sulphate, 
8 gm.; in two 
applications. 
Gm. 
Gm. 
Gm. 
Gm. 
( 11.2 
6.3 
6.9 
8.9 
18.4 
16.9 
13.4 
18.7 
28.8 
32.5 
37.2 
33.9 
56.2 
34.1 
49.3 
50.8 
69.2 
68.9 
61.1 
59.8 
86.1 
86.6 
84.3 
87.4 
42.6 
37.1 
44.4 
33.0 
63.1 
61.1 
56.1 
64.1 
9.9 
6.7 
9.3 
8.2 
{ 50.2 
47.0 
41.7 
50.2 
Gm. 
5.9 
9.5 
21.7 
45.6 
61.2 
89.6 
30.8 
46.3 
7.3 
45.2 
Gm. 
7.8±0.7 
15.4±1.1 
30.8±1.8 
47.2±2.5 
64.0±1.4 
86. 8± .6 
37.6±1.8 
58.1±2.2 
8.3± .4 
46.9±1.1 
30 
