21 
EXPERIMENT IV. 
Hawaiian soils contain abnormally large quantities of iron and 
aluminum. Investigators have attributed the unavailability of phos- 
phoric acid in soils directly to the presence of these two elements, 
and it is quite generally held that the presence of adequate amounts 
of lime will prevent phosphates from combining with iron and alumi- 
num. The first series of pots in Experiment IV, therefore, was 
planned to determine what influence the lime has on the availability 
of phosphoric acid in the soils. This series of pots was divided into 
two main groups, one receiving no lime, the other being limed at the 
rate of 0.10 per cent calcium carbonate in excess of the lime require- 
ment as determined by the Veitch method. 
The same three soils were used in this series as in previous experi- 
ments. Some of the pots were green manured with legumes, as indi- 
cated in the second column. The data are presented in the same 
manner as in the previous tables. Only one crop of millet was 
grown in soil No. 1, but the tests upon soils Nos. 2 and 3 were repeated 
by a second planting. The results are given in Table VI. 
The addition of lime to soil No. 1 caused only a slight increase in 
growth of the plants. Probably this was due to the high percentages 
of lime and magnesia already present in this soil. 
In soil No. 3 a large increase followed the application of lime with 
the soluble phosphates, but not its application with phosphate rock, 
This indicates that lime assists the plants in assimilating phosphoric 
acid, but whether this is a chemical or physical phenomenon is yet 
to be proved. 
In soil No. 2 the effect of lime was much more striking. Here the 
growth of millet was increased in every instance where lime was ap- 
plied with the phosphates. This soil is a heavy clay type; No. 3 
contains much less clay, and No. 1 the least clay. It is entirely pos- 
sible that there is a relation between the influence of the lime and the 
amount of clay present in the soil. The most striking effect of the 
lime in case of soil No. 2 was upon the character of the plant. In all 
pots without lime, the millet came up in clumps like grass and grew 
to a height of only about 6 inches, while the addition of lime produced 
normal plants. 
On replanting the millet in soils Nos. 2 and 3 the results were 
somewhat different. The lime had apparently lost its influence in 
most cases, more especially in soil No. 3, which contained less clay. 
The second part of Experiment IV was planned to determine the 
availability of ferrous, ferric, and aluminum phosphates as com- 
pared with the other phosphates. Soils Nos. 2 and 3 were used in 
this work, the results of which are given in Table VII. 
