32 BULLETIN 31, PORTO RICO EXPERIMENT STATION 
The results of the test indicate that if sodium nitrate is used as a 
fertilizer for coffee it should be given in small quantities at short 
intervals rather than_in larger quantities at longer intervals, and 
also that sulphur should be supplied in addition. 
SUMMARY AND SUGGESTIONS 
In the experiments reported in this bulletin nitrogen, phosphoric 
acid, and potash, singly and in combination, were applied to coffee 
trees through a series of years and their effects on growth and yield 
noted. 
In a planting of 40 small plats the general trend of future per- 
formance as affected by fertilization was indicated as early as the 
first important crop. The production over an 8-year period 
showed that potash was effective in increasing yield, and that this 
was true particularly where nitrogen was used in addition to potash. 
Heavy applications of nitrogen unaccompanied by potash very ad- 
versely affected growth and fruiting, whereas the same quantity of 
nitrogen in conjunction with potash proved beneficial rather than 
injurious, trees so fertilized developing luxuriant foliage and heavy 
crops of fruit. The plat ranking first in yield received this fertilizer 
combination at the maximum rate. Analyses of the soil solution 
showed this plat to be higher in acidity than any in the field, thus 
placing coffee among the acid-tolerant crops. Growth and yield 
failed to show that the addition of phosphoric acid was of benefit. 
Growth and yield were closely correlated. 
In several other series of plats use of complete fertilizer resulted 
in all cases in moderate to pronounced increase in yield. In one 
series the yield from the plat receiving complete fertilizer was ap- 
proximately three times as great as from the check plat for a 13-year 
period. On this soil all three elements were necessary for maximum 
vields. 
The size of the coffee cherry was observed to be related to the 
yield, a notable increase in yield being accompanied by a slight re- 
duction in size of cherry. The only observed effect of fertilizer on 
size was thus indirect. 
In field tests nitrogen appeared to increase early production. In 
various pot tests it greatly stimulated growth, as was shown by a 
large increase in number of leaves, in weight of foliage, stem, and 
roots, and in height. Although the number of leaves was increased, 
no correlation was observed between leaf length and kind of fertilizer 
applied. 
In both field and pot tests ammonium sulphate, applied semi- 
annually, proved much more effective than sodium nitrate in in- 
creasing both growth and yield in a planting of Bourbon coffee. 
In cooperative experiments with sodium nitrate alone, applied 
semiannually for two years on one plantation and four on another, 
no increase in yield attributable to its use was observed. On the 
latter plantation a change in fertilizer treatment involving the use 
of ammonium sulphate and sodium nitrate each singly and in com- 
plete fertilizer was followed by an increase in the yield of the plats 
receiving complete fertilizer. The effectiveness of ammonium sul- 
phate alone was less pronounced and no benefit whatever was ob- 
