17 
maturity. Phosphate rock again, as in the original application, 
proved the least available. The other phosphates were quite similar 
in their action, and all were more effective than phosphate rock. 
Large applications of the latter were little more effective than small 
applications. 
EXPERIMENT III. 
In view of the fact that the soil used in Experiments I and II was 
deficient in phosphoric acid, two soils less deficient in this constituent 
and of a much better mechanical texture were chosen for further tests. 
In soil No. I the phosphates had little influence upon plant growth, 
for which reason only one planting was made. In soil No. 3 there 
was a slight effect, and two crops were grown in this series. In the 
red clay soil (No. 2), the plants did not stool, but in soils Nos. 1 and 3 
there was excessive stooling, and for this reason the number of stools 
as well as of plants is indicated in the tables. 
The treatment of the pots was somewhat modified as follows: 
Only one slag was used in this series, and additions were made of 
trimagnesium phosphate, tripotassium phosphate, dipotassium phos- 
phate, monopotaSsium phosphate, reverted phosphate, and bone meal. 
The pots of soil No. 1 were seeded June 18 and harvested September 
10. Those of soil No. 3 were seeded June 23 and harvested Septem- 
ber 18; they were then aerated, mixed, and replanted to millet 
October 12, and harvested January 11. The results are given in 
Table V. 
All pots of soil No. 1 produced an excellent growth of millet re- 
gardless of fertilizer. The growth in the pots containing sodium phos- 
phate was slightly greater than in the other pots, but this soil showed 
itself to be very high in available phosphate. 
Soil No. 3 proved to be slightly deficient in available phosphoric 
acid, and an increase in plant growth resulted from all phosphate 
applications. Phosphate rock was again the least effective of all the 
phosphates. Sodium phosphate and superphosphate produced the 
largest increase, while the results from slags and acid were very 
good. Reverted phosphate and bone meal were very ineffective. 
The monobasic, dibasic, and tribasic potassium phosphates were 
used to determine, if possible, any influence due to basicity of the 
salt, but no such relation was apparent. 
The second millet crop on soil No. 3 gave very little information of 
additional value. In this crop the plants did not stool, and partly 
for this reason the weight of the plants was considerably reduced; 
hence the decrease in plant growth noted here must be attributed 
primarily to seasonal factors, although removal of readily available 
phosphate may have been a minor factor. Phosphate rock proved 
to be a very ineffective form of phosphate, and the soluble phosphates 
gave the best results. 
61185°— 16 3 
