8 
BULLETIN 31, PORTO RICO EXPERIMENT STATION 
Table 4. — Comparison of average production of trees receiving any one fer- 
tilizer element and of those failing to receive that element, South Field plats 
Yield of cherries with the different fertilizer treatments 
Year 
Nitrogen 
Check 
Phos- 
phoric 
acid 
Check 
1 
Potash Check 
1917 
Grams 
1,007 
1,564 
636 
1,164 
1,998 
1,567 
3,092 
4,083 
Grams 
936 
1,168 
447 i 
637 ' 
1,810 
1,547 
3,185 ; 
4,747 
Grams 
911 
1,308 
460 
897 
1,583 
1,393 
2,677 
4,152 
Grams 
1,031 
1,419 
620 
905 
2,209 
1,713 
3,590 
4,676 
Grams Grams 
1 160 782 
1918. 
1 812 ,Q23 
1919 
699 377 
1920. 
1 275 498 
1921 
2, 251 1, 525 
2, 236 811 
3,925 2,272 
5,611 3,207 
1922 
1923 
1924... 
Total. 
15, 111 
104 
14, 477 
100 
13, 381 
83 
16, 163 
100 
18, 969 10, 395 
182 100 
Percentage in respect to check 
Figure 7 shows the curves for the sections. 
CHANGES IN THE SOIL SOLUTION AS A RESULT OF THE FERTILIZER TREATMENTS 
Examination of changes in the soil solution of the plats was made 
by J. O. Carrero, assistant chemist of the station. His report follows : 
The different fertilizer treatments continued through a period of years offered 
an opportunity to observe resulting changes in the soil solution. Six smaller, 
followed by 15 full fertilizer applications, made at intervals of six months, 
preceded taking the soil samples. Shortly prior to the fertilization of May, 
1925, soil samples were taken from the upper 6 to 8 inches, and air dried 
and ground previous to testing. The acidity of the soil of the different plats 
as determined by the hydrogen-ion concentration in the soil extract is shown in 
Table 5. 
Table 5. — Soil acidity of the differently fertilized plats as shown by the hydro- 
gen-ion concentration in the soil extract 1 
Rate of 
fertilizer 
applica- 
tion per 
tree 

Plats receiving— 
Division 
K 
P 
N 
NK 
PK 
NP 
NPK 

1 
Pounds 
H 
H 
l 
2 
4 
pH+ 
7.0 
6.6 
7.3 
7.1 
7.2 
pH+ 
6.9 
6.7 
6.6 
6.7 
6.7 
pH+ 
7.1 
6.7 
6.8 
6.8 
6.8 
PH+ 
6.8 
6.5 
6.1 
5.8 
5.7 
pH+ 
7.2 
6.8 
6.8 
6.9 
7.0 
pH+ 
7.1 
6.6 
6.6 
6.7 
6.1 
pH+ 
6.8 
6.3 
6.2 
6.1 
6.2 
pH+ 
7.2 
2 
7.3 
3 
7.3 
4 
7.2 
5 
7.4 
i Clark and Lub's colorimetric method was used to determine acidity. 
The soil reaction was the same for the five untreated plats. The plats to 
which potassium sulphate alone was applied, even in the maximum quantities, 
showed no change in reaction. Ammonium sulphate alone, and acid phosphate 
alone and in combination with potassium sulphate, only very slightly increased 
soil acidity. The increase was the same for the three treatments, and was as 
great for the one-half pound application as for the 1, 2, or 4 pound applica- 
tions. A greater increase in acidity was produced by ammonium sulphate and 
acid phosphate in combination and by the complete fertilizer. In the former 
instance the one-half pound was as effective as the 1 and 2 pound applications, 
but there was a sharp increase in acidity with the 4-pound application. Where 
the complete fertilizer was given, the 1, 2, and 4 pound rates caused little 
increase in acidity over the one-half-pound rate. 
