47 ' 
that of bone meal under the same conditions. Nearly all guanos had a 
higher immediate efficiency than ground rock phosphate, although 
in a few instances this was lower. 
The guanos were equally efficient for corn and millet, and there 
was no evidence of their being any more efficient for rice. 
Four guanos gave the same efficiency (relative to acid phosphate) 
in a clay soil as in a sand, while eight samples were from 30 to 1,100 
per cent more effective in the clay than in the sand. Bone meal and 
floats also showed increased efficiency in the clay. 
Remaining in the soil six weeks before planting the crop slightly 
increased the efficiency of some guanos, slightly depressed that of 
others, and markedly depressed the efficiency of acid phosphate. 
Bone meal and floats lost very slightly in efficiency by remaining in 
the sand but increased markedly by remaining in the clay. Liming 
tended to counteract the effect of the soil on availability. 
Liming the soil had a practically negative effect on the efficiencies 
of four guanos, but markedly depressed the availability of acid 
phosphate. Relative to acid phosphate these four guanos therefore 
showed increased efficiencies in the limed soil. Seven other guanos 
suffered a marked to an extreme loss of availability in the limed soil. 
Bone meal and floats also lost more in availability than acid phos- 
phate in the limed soil, while slag and acid phosphate were affected 
about equally. Liming the red clay depressed availabilities more 
than liming the sandy soil. 
It was found that the quantity of guano used did not affect the 
availability of its phosphoric acid. Consequently even guanos of low 
efficiency will produce maximum yields if they are used in sufficient 
quantities. 
The guanos seemed to be equally efficient at all stages of crop 
growth so far as assimilation by the plant was concerned. However, 
most guanos would show a greater availability relative to acid phos- 
phate with a long-time crop than with a quick crop, as most guanos 
were little affected by remaining in the soil while the availability of 
acid phosphate was decreased. This is an important consideration 
under Porto Rican conditions, as cane, citrus fruits, and pineapples 
are long-time crops. 
It was shown that solubility of the phosphoric acid in neutral 
ammonium citrate was a fair measure of the available phosphoric 
acid in about 70 per cent of the guanos tested, but an inaccurate 
method for some samples. 
EXPERIMENTS ON EFFICIENCY OF THE NITROGEN IN GUANOS. 
Plan of experiments and materials used. — In testing the efficiency of 
nitrogen in guanos the same plan was used as in the work on phos- 
phoric acid. Work on nitrogen was on a less extensive scale than 
