FERTILIZERS FOR COFFEE IN PORTO RICO 
15 
As has been the case with many other coffee plantings at the sta- 
tion, 4 the trees on the upper slope grew slowly, whereas those on the 
lower grew vigorously. That growth was greatly influenced by an- 
other factor as well was shown by measurements of height taken in 
January, 1920 (fig. 10) , and of trunk diameter made in August, 1921. 
All rows treated with ammonium sulphate except one surpassed in 
height the highest row treated with sodium nitrate. The total height 
of the former was 28 per cent greater than that of the rows treated 
with sodium nitrate. Figure 11 graphically shows the trunk diame- 
ters and also the pronounced effect of the form in which nitrogen 
was applied. Use of ammonium sulphate resulted in an increase in 
yield of 63 per cent for the 7-year period, and fully demonstrated its 
superiority over sodium nitrate under the conditions of the test. It 
is not known what benefit may have been derived from sodium nitrate 
since there was no unfertilized check plat. Table 7 shows the annual 
yields of the two plats. 
Table 7. — Comparative yields of Bourbon coffee cherries on plats receiving 
ammonium sulphate and sodium nitrate 
Year applied 
Plat 1, 
ammo- 
nium 
sulphate 
Plat 2, 
sodium 
nitrate 
Yield of 
plat 1 in 
percent- 
age of 
plat 2 
1918 
Liters 
5.5 
43.5 
60.6 
152.3 
89.3 
217.3 
127.7 
Liters 
4.2 
30.1 
14.9 
88.4 
57.8 
136.6 
94.1 
Per cent 
131 
1919 
145 
1920 
407 
1921 
172 
1922 
154 
1923 .• 
159 
1924 
136 
Total 
696.2 
426.1 163 
BISCHOFF AND LOPEZ PLANTATION PLATS 
Field tests on the Bischoff and Lopez plantations were undertaken 
to ascertain the effectiveness of sodium nitrate as a fertilizer for 
coffee. 5 Later, comparative tests of ammonium sulphate were added. 
On the Bischoff plantation two ^-acre plats were fertilized with 
sodium nitrate at the rates of 150 (plat 1) and 300 (plat 3) pounds, 
respectively, per acre per application. Between the two lay a ■£$- 
acre plat (plat 2), which was used as a check as uniform trees were 
not available for three j^-acre plats. The soil was red clay covered 
with an abundant natural mulch derived from a uniform and suit- 
able shade. The coffee trees were said to have been set 4 years 
previously, and were apparently lacking in vigor. Sodium nitrate 
was applied in February, July, and December, 1916, and again in 
June and December, 1917. Crop yields were recorded in pounds. In 
the fall of 1916, plat 1 yielded an average of 2 pounds per tree, plat 
2 jdelded 2.1 pounds, and plat 3, 2.2 pounds. In 1917, plat 1 yielded 
an average of 1 pound per tree, plat 2, 1.3 pounds, and plat 3, 1.2 
4 Porto Rico Sta. Bui. 21, Some Profitable and Unprofitable Coffee Lands. 
5 Originally carried on in cooperation with Chilean Nitrate Propaganda Agency. 
