21 
Corn (Zea mays), millet (Setaria italica), and rice (Oryza sativa) 
were the crops used. Millet and rice were grown to maturity, and 
transplanted corn seedlings were grown 30 to 40 days. 
The fertilizing materials were mixed with the first 3 or 4 inches of 
soil in each pot before planting. When a second application of the 
basic fertilizer was used, it was applied to the surface in dilute 
solution. 
EXPERIMENTS ON EFFICIENCY OF PHOSPHORIC ACID IN BAT GUANOS. 
Plan of experiments and materials used. — In testing the efficiencies 
of the different guanos as phosphatic fertilizers it was necessary to 
conduct the work in considerable detail on account of the many 
factors affecting the availabilities of phosphatic fertilizers. The 
relative efficiencies of different phosphates are known to vary some- 
what with the kind of soil and crop, and to be differently affected by 
liming. There is also supposed to be a difference between the 
efficiencies of phosphates applied immediately to the crop and those 
applied sometime before- the crop is planted. Certain representative 
samples of guano were tested with respect to these variable con- 
ditions of soil, crops, liming, and effect of remaining in the soil. 
Most of the samples, however, were tested only for their immediate 
availability or efficiency in one soil, the river sand. 
In the following tests two soils deficient in phosphoric acid were 
used, a river sand x and the Porto Rican red clay. 2 The red clay, 
fully described elsewhere, is acid and consists almost entirely of silt 
and clay particles. The river sand is neutral in reaction and con- 
tains considerable coarse and medium sand and a small amount of 
clay particles. It is doubtless derived from clay soil as the river 
which deposits it drains a red clay area. 
The guanos were all compared with acid phosphate as a standard, 
but bone meal, basic slag, finely ground rock phosphate or floats, and 
a leached bird guano from Mona Island were also used in many tests 
to afford a better idea of the position of bat guanos among phos- 
phatic fertilizers in general. Analyses of these materials are given 
in Table VII. 
i Porto Rico Sta. Bui. 11 (1911), p. 22. J Porto Rico Sta. Bui. 14 (1914). 
