192 
Journal of Agricultural Research 
Vol. XXV, No * 
tions that have been made of the “residual” or “after-effects” of phos- 
phatic applications have not been so conducted as to throw much light 
on this subject. 7 
That such losses in efficiency or in “availability” may be very consid¬ 
erable and very general seems to be indicated by the fact that as a rule 
only a small portion of the phosphoric acid applied to the soil is recovered 
in the crop. While recoveries in the crop of 60 to 90 per cent of the 
nitrogen or potash applied are common, recoveries of phosphoric acid 
usually range much lower—from 10 to 20 per cent (15), or sometimes 
even 2 per cent. That this low recovery of phosphoric acid is due to 
interaction between phosphates and certain soil constituents is indicated 
by the experiments of Pfeiffer and Simmermacher (20) in quartz sand. 
SUMMARY 
(1) The relative efficiencies of acid phosphate, rock phosphate, bone 
meal, basic slag, and double superphosphate were tested in nine different 
soils in which millet was grown as the crop. The effect of the length of 
time the phosphates remained in the soil and the influence of liming on 
the relative efficiencies of the phosphates were also determined. 
(2) The relative efficiencies of all the phosphates varied widely in the 
different soils. Bone meal and rock phosphate were particularly affected 
by the character of the soil. In one soil the efficiency of rock phosphate 
was about the same as that of acid phosphate, while in another soil it 
was only 4 per cent that of acid phosphate. 
(3) None of the phosphates varied in efficiency directly with the lime 
requirement of the soil, although rock phosphate and bone meal were 
generally most effective in the soils with high lime requirements. 
(4) Applications of lime equivalent to the lime requirement of the 
soil (determined by the Veitch method) decreased the efficiencies of acid 
phosphates, basic slag, and double superphosphate in some soils and 
increased them slightly in others. In two soils liming had little influence 
on bone meal, but in the seven other soils it markedly decreased the 
efficiency of the bone meal. The efficiency of rock phosphate was 
decreased by liming to an approximately constant value in all soils— 
about 3 per cent that of acid phosphate. 
(5) Practically no difference in efficiency was observed regardless of 
whether the lime was applied to the soil six weeks before or immediately 
before the phosphate was applied. 
(6) A considerable further decrease in the efficiency of bone meal 
occurred when the quantity of lime applied was increased beyond the 
amount indicated by the lime requirement of the soil. 
(7) It is probable that even in those soils where the efficiencies of acid 
phosphate, basic slag, and double superphosphate were increased by 
the quantity of lime applied a larger application of lime would have 
decreased the efficiencies of these materials. 
(8) A comparison was made of the efficiencies of the phosphates 
applied six weeks before planting with the efficiencies of the materials 
applied immediately before planting. When the phosphates remained 
six weeks in the soil the efficiencies of the five phosphates diminished 
very appreciably in all soils whether limed or not. The losses in effi¬ 
ciency attributable to the phosphates remaining in the soil were greater 
7 This is chiefly due to the fact that the crop residues have not been removed before the second crop was 
planted, and it is therefore impossible to ascertain how much of the phosphoric acid assimilated by the sec¬ 
ond crop was secured from the decomposition of the organic residues of the first crop and how much from 
the unassimilated phosphoric acid left in the soil 
