FERTILIZERS FOR COFFEE IN PORTO RICO 
9 
The maximum change in soil reaction was produced by ammonium sulphate 
and potassium sulphate in combination. Here there was a continuous increase 
in acidity in harmony with the rate of application. The plat showing the 
highest acidity also held the record for maximum production. As yet this 
acidity has shown no unfavorable effects on either growth or yield. The length 
of time required for acidity to increase to the point of injury under continued 
heavy applications has not as yet been determined. 
The different fertilizers affected differently the physical condition of the 
soil, as is shown by the rate at which the soil particles settled when they were 
shaken with water. Acid phosphate was the most effective agent in floccula- 
tion. The soil particles of samples from plats which were treated with acid 
phosphate, either alone or in combination, when well shaken with water settled 
PO/NTS DETEPMt/VED BY TPEES IN 
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Fig. 4. — Average production per tree for the year 1924. South Field plats 
in 6 to 10 hours, leaving a clear solution above, whereas samples from the un- 
treated plats were still muddy at 36 to 40 hours after shaking. Second to acid 
phosphate plats came those receiving ammonium sulphate and potassium sul- 
phate in combination at the two heaviest application rates, this effect not 
following the lighter applications, however. There was only a slight improve- 
ment in flocculation in the plats treated with ammonium sulphate alone and 
no improvement in those treated with potassium sulphate alone. 
PADANG AND ERECTA PLATS 
In contrast with the uniformity of slope found in the West Field 
plats, the Padang and Erecta plantings are on rather steep slopes, 
11834—26 2 
