July 28,1923 
Efficiency of Phosphatic Fertilizer 
183 
3 per cent of the efficiency of acid phosphate for the gramineae. It is 
possible that this value represents the relative efficiencies of floats and 
acid phosphate in soils which do not contain compounds unsaturated 
with calcium. 
Bone meal varied more in efficiency than did any other phosphate 
according to the character of the soil. In soils No. 1796, 1524, and 1529 
it had an efficiency equal to, or greater than, acid phosphate when no 
lime was applied, while in soils No. 1810, 1811, and 213 it was only 
about one-third as effective as acid phosphate. In all the limed soils 
except No. 1716 it was rather an ineffective source of phosphoric acid. 
When the results obtained with basic slag are considered, it should be 
borne in mind that this material was compared with the other phosphates 
on the basis of its total phosphoric acid content, although it is sold on the 
basis of its “available” phosphoric acid. In the slag used in the experi¬ 
ments 78 per cent of the total phosphoric acid was soluble in 2 per cent 
citric acid, that is, “available” by the Wagner method. Considered on 
the basis of its available phosphoric acid, basic slag was more efficient, 
on the whole, than was acid phosphate, since in the nine unlimed soils 
it averaged 87 per cent as efficient as acid phosphate when applied 
immediately before planting was done. Basic slag was also very effective 
when it was applied six weeks before planting and when it was used in 
conjunction with lime. 
The efficiency of the phosphoric acid in double superphosphate was 
practically the same as that in acid phosphate. 
It might be expected that the efficiencies of certain phosphates would 
depend to a considerable extent upon those qualities of the soil which are 
indicated by the lime requirement. Apparently, however, this is not so. 
Table VI shows the lime requirements of the soils and the efficiencies of 
the different phosphates in the soils when applied immediately before 
planting without the use of lime. The efficiency of each phosphate is 
expressed relative to 100 for the efficiency of acid phosphate applied 
under the same conditions, except in the case of soil No. 1529. In the 
case of this soil the efficiency of each phosphate is expressed relative to 52 
for the efficiency of acid phosphate, since acid phosphate was relatively 
ineffective in this soil without lime. (See Table V.) 
Tabi^E VI .—Showing the relation between the lime requirements of the soils and the relative 
efficiencies of the phosphates 
Soil No. 
Eime 
(CaO) re¬ 
quired to 
neutralize 
soil. 1 
Efficiency of— 
Floats. 
Bone 
meal. 
Basic 
slag. 
Double 
superphos¬ 
phates. 
1810... 
O. 272 
34 
43 
92 
83 
1796. 
. 196 
46 
98 
80 
86 
1578. 
. 176 
20 
72 
94 
IOI 
1257 . 
. 108 
22 
51 
71 
87 
1524 . 
. 103 
10 
105 
ill 
85 
1811. 
♦075 
15 
33 
69 
97 
1529 .. 
.056 
79 
78 
IOO 
56 
1716. 
. 006 
8 
72 
105 
IOO 
1 Expressed in percentage of soil. 
