YAM CULTURE IN PORTO RICO. 9 
Average yield, in pound* per lull, ridge planting, of four varieties of yams on 
fertilized and unfertilized plats during the years named. 1 
Fertilizers applied. 
Variety. 
Stable 
manure. 
Phos- 
phorus 
and 
potash. 
Phos- 
phorus 
and 
nitrogen. 
Potash 
and 
nitrogen. 
Phos- 
phorus, 
potash, 
and 
nitrogen. 
Check. 
Potato: 
In 1913 
Pounds. 
3.9 
1.6 
3.4 
1.57 
Pounds. 
4.05 
1.6 
3.4 
1.41 
Pounds. 
3.55 
2.4 
3.15 
1.78 
Pounds. 
3.6 
1.6 
4.33 
2.12 
Pounds. 
5.17 
3.6 
4.23 
2.82 
Pounds. 
3.45 
In 1914 
2.3 
In 1915 
3.23 
In 1916 
1.84 
Average 
2.62 
2.62 
2.72 
2.91 
3.95 
2.75 
Barbados: 
In 1913 
8.4 
7 
4.8 
7.1 
4.5 
4.5 
6.5 
6.2 
5 
4.1 
3.4 
6.36 
7 
7 
5.5 
4.8 
In 1914 
5.9 
In 1915 
4 
Average 
6.73 
5.37 
5.9 
4.62 
6.5 
4.9 
Guinea: 
In 1913 
3.17 
.6 
1.2 

3.17 2.83 
2.4 2.1 
.54 .96 
3 
2.1 
1.04 
4.8 
1.1 
10.4 
3.33 
In 1914 
1.7 
In 1915 
1.7 
Average 
1.66 
2.03 
1.96 
2.05 
5.43 
2.24 
Agua: 
In 1913 
3.37 
4.2 
2.2 
1.8 
4.5 
2.5 
2.4 
1.4 
4 
1.4 
3.3 
3.3 
4.2 
3 
3 
1.7 
4.62 
2.5 
4.6 
3.05 
4 
In 1914 
3.4 
In 1915 
3.3 
In 1916 
1.9 
Average 
2.89 
2.7 3 
2.97 
3.69 
3.15 
Average for four varieties 
3. 475 
3.18 3.395 3.14 
4.89 
3.26 
1 Each plat wa 
s about on 
e-twentiet 
h acre in s 
ize. 
This table shows that there was a wide range in yield of each 
variety in the different plats during a given year, and that large dif- 
ferences were not consistent for all the plantings; also that the dif- 
ferent fertilizers produced only small differences in the average yield 
of a number of crops. Where all three chemical ingredients were 
given, the average production for all varieties combined was consid- 
erably higher than where one element was omitted. It was also 
higher than where stable manure was given in all except the Barba- 
dos variety, where the yield from stable manure slightly exceeded 
it. Where all three elements were given, the plat made a gain of 
more than 50 per cent over the check. In the test where nitrogen 
was omitted and in that where phosphorus was omitted, the total 
average yields were less than where no fertilizers were given. The 
plat receiving no nitrogen gave a lower combined average produc- 
tion than any other plat except the one receiving no phosphorus. 
The combined average production by the plat treated with stable 
manure was greater than that of any other plat except the one receiv- 
ing a complete chemical fertilizer, which exceeded it by 40 per cent. 
As the application of only two of the three elements — nitrogen, phos- 
27764°— 21 2 
