31 
soluble, that is, it supplies soluble phosphoric acid at a faster rate. 
Without attempting a detailed discussion of a subject which still 
needs investigation, it may be pointed out that, whether or not 
different crops have different powers of " feeding" on insoluble 
phosphates, it is well established that one phosphate may be much 
more effective than another for a certain crop. 
Table IX has been compiled from the figures in Tables VIII and X 
to XV. 
Table IX. — Effect of crop on the availability of phosphoric acid in guanos. 
Source of phosphoric 
acid (P 2 5 ). 
Crop. 
Efficiency 
of phos- 
phoric acid 
compared 
with that of 
acid phos- 
phate= 100. 
Source of phosphoric 
acid (P 2 5 ). 
Crop. 
Efficiency 
of phos- 
phoric acid 
compared 
with that of 
acid phos- 
phate= 100. 
/Millet 
29 
29 
19 
13 
23 
a 27 
17 
a 17 
9 
9 
53 
a 75 

a 1 
12 
a5 
25 
a 30 
2 
a2 
4 
a3 
Guano No. 733 
Guano No. 750 
Guano No. 780 
Guano No. 785 
Guano No. 797 
Guano No. 810 
Guano No. 811 
Guano No. 819 
Floats 
/Millet 
60 
Guano No. 263 
\Corn 
\Corn 
68 
/Millet 
/Millet .. 
6 
Guano No. 497 
\Corn 
\Corn 
oil 
/Millet 
fMillet 
77 
Guano No. 498 
\Corn 
76 
/Millet 
/Millet 
38 
Guano No. 501 
\Corn 
39 
/Millet 
/Millet 
20 
Guano No. 502 
\Corn 
18 
/Millet 
fMillet 
11 
Guano No. 503 
\Corn 
8 
/Millet 
fMillet 
15 
Guano No. 504 
\Corn 
14 
/Millet 
|Millet 
65 
Guano No. 506 
\Corn 
66 
/Millet 
/Millet 
«4 
Guano No. 507 
06 
«65 
/Millet 
Slag 
fMillet 
Guano No. 508 
\Corn 
Bone meal 
/Millet 
/Millet 
a29 
Guano No. 509 
\Corn 
\Corn 
o Average from several determinations. 
In the above table comparisons are given of the efficiencies of bone 
meal, slag, floats, and 19 different guanos for corn and millet. In 
50 per cent of the cases the difference between the efficiencies for 
corn and millet was 3 or less, the average for the efficiencies of the 
22 samples being 27 for millet and 29 for corn. It is therefore 
apparent that the guanos are equally effective for corn and millet. 
The effectiveness of guanos for rice was also tried, but as the 
growth of rioe was increased only 20 per cent by abundant phos- 
phoric acid, few efficiencies could be calculated. Guanos Nos. 502, 
505, 506, and 508 showed no availability for rice in this test. In 
this same lot of soil, the growth of corn was increased 300 per cent 
by phosphatic fertilization and the same guanos which had no 
availability for rice had a very low availability or none for corn. 
This test demonstrates how much less rice responds to phosphatic 
fertilization than corn and shows no greater ability in rice to utilize 
insoluble phosphates than in corn or millet. 
