4 BULLETIN 27, PORTO RICO EXPERIMENT STATION. 
The yam has been grown in all parts of Porto Rico for many years, 
cultural practices having developed in accordance with local needs. 
Little progress has been made in adopting improved methods of 
culture or in introducing or disseminating imported varieties. Ex- 
periments having in view the introduction of new and improved va- 
rieties and methods of culture have been in progress at the experi- 
ment station for a number of years. 
GENERAL PRACTICES IN YAM GROWING. 
The kinds of yams commonly grown in Porto Rico are not par- 
ticularly sensitive to the type of soil in which they grow, provided 
the weather conditions are favorable and the proper cultural prac- 
tice is followed. They are most prolific, however, in a deep, 
fertile clay, and give poorest yields in light, sandy soils. Some 
varieties make good yields when grown in heavy, sandy loams. 
Other varieties yield very well in the heaviest clays where the ridges 
are sufficiently high to enable the plant to develop a good root sys- 
tem. Compacted and wet soil hinders the growth of the plant and 
prevents normal root development. Where ridge planting is prac- 
ticed the roots make a normal growth above the zone of wet soil. 
In all frost-free countries yams may be planted at any time of 
the year, though not always profitably in a long rainy season, nor 
where there is a protracted drought such as sometimes occurs in 
Porto Rico and other islands of the West Indies. During the season 
of rains the heavy wet soil tends to hasten any decay that has started 
in the seed yams, and too frequent rains retard and stunt the growth 
of the young plants. On the other hand, a long dry season, if it is 
followed by drought, is even more detrimental to them. Young 
plants set out in the dry season may not obtain sufficient nutriment to 
continue growth after the supply in the seed tuber is consumed. 
The best time to plant in western and southern Porto Rico, and 
probably through this island, is after the usual winter drought — 
that is, from late February to April — when the soil has been left in 
good condition for planting by the spring rains. Normal growth 
is then assured. Fall plantings should be made after the time of 
most frequent rains, but while they are still sufficiently abundant 
to cause a thrifty growth of the young plants. This particular 
period is during the last of November in Mayaguez, where the sea- 
sons are well defined. 
The crop which is planted in the spring matures late in the fall 
and winter, and may be left in the ground during the dry winter 
without fear of deterioration. This crop is available for table use 
through a long period or for disposal at a satisfactory price, de- 
pending upon the demands of the local market. Yams intended 
