41 
In regard to absolute gain or loss in availability (comparison of 
values in third and fifth columns), it can be seen that guanos Nos. 
811 A, 923, 957, and 966B were practically unaffected by liming; 
while all other guanos, together with bone meal, floats, and slag, 
suffered moderate to extreme losses in availability. 
Liming decreased the efficiency of the phosphates more in the red 
clay than in the sand. This was due to the fact that certain materials 
have an enhanced availability in the acid clay (see Table XI). The 
degree to which liming affects the efficiency of phosphates thus de- 
pends largely on the nature of the soil as well as on the character of 
the phosphate. 
The influence of lime on the efficiencies of phosphates applied to 
the soil six weeks before planting was pointed out on page 38. 
Effect of quantity of guano used on efficiency of the phosphoric 
acid. — In the preceding tests some of the guanos had a very low 
availability, only 2 to 10 per cent of that of acid phosphate. It 
was expected that the availability of such materials would be inde- 
pendent of the quantity used in the experiment; nevertheless this 
point was tested, as it is of considerable practical importance. If 
the availability of the materials is independent of the quantity 
used, then a maximum effect can be secured if a sufficient quantity 
is used. 
Table VIII affords detailed results of tests of several different 
quantities of the same guano, summarized results being given in 
Table XVII. 
Table XVII. — Effect of quantity of guano used on immediate availability of phosphoric 
acid in guanos. 
Source of phosphoric acid 
(P 2 5 ). 
Phosphoric 
acid applied 
per pot. 
Efficiency 
of phos- 
phoric acid 
compared 
with that of 
acid phos- 
phate=100. 
Source of phosphoric acid 
(P 2 5 ). 
Phosphoric 
acid applied 
per pot. 
Efficiency 
of phos- 
phoric acid 
compared 
with that of 
acid phos- 
phate=100. 
Grams. 
J 3.6 
\ 14.4 
f 3.6 
7.2 
j 14.4 
I 28.8 
2 
1 
2 
3 
3 
2 
Guano No. 734 
Grams, 
f 1.2 
1.8 
2.7 
4.05 
/ 6.0 
\ 18.0 
39 
36 
Floats 
30 
45 
7 
4 
Where availabilities varied with the quantity of guano applied, 
the differences were within the limits of experimental error. The 
results as a whole show that the availability of the guanos is main- 
tained when large amounts are used and, therefore, if applied in 
sufficient quantity, they will produce the same increased yield as 
commercial phosphates. 
