412 
The Philippine Journal of Science 
1921 
FERTILIZATION 
A most interesting system of soil conservation and fertiliz- 
ation is practiced by the growers. This consists of cleaning out 
from the trenches’ all organic matter and clay that may have 
rotted and accumulated there. Dead leaves, straw, branches, 
and other refuse naturally find their way to the bottom of these 
trenches where they decay, and by this process are made useful 
for fertilizer. All organic matter is carefully conserved, and 
one often sees under the trees (Plate 9, fig. 2) rice or sugar-cane 
leaves which, if they are not washed into the trenches, will soon 
be covered over with a coating of mud. 
Canal mud is still more fertile than the mud in the trenches, 
and a practice very common in China is followed here also. 
During the dry weather, when the canals are low, mud from 
the bottom is removed, placed along the sides of the dikes, and 
allowed to dry in blocks. After the mud is thoroughly sun- 
dried, it is broken into pieces and carried in baskets to the 
citrus trees and distributed at the rate of about two large bas- 
ketfuls to each tree. From what has already been said regard- 
ing the rise of water in the trenches, it is evident that the trees 
under this culture develop a surface root system. This fertile 
canal mud, together with the mud from the trenches, helps to 
keep these roots from exposure and to provide an important 
source of plant food. 
Nakorn Chaisri pummelo growers recognize that the quality 
of the fruit is greatly influenced, not only by soil and water 
conditions, but also by artificial fertilization. Some very inter- 
esting theories have developed regarding the effect of salt and 
paddy ash upon the seediness and what is known as the kao sam, 
or raw-rice, condition of the fruit. 
One grower in the Dao Kanong region stated that, if salt and 
paddy ash are applied to trees bearing bitter fruits or fruits 
lacking in juiciness, the fruits of the following year would be 
much less bitter and more juicy. It was also mentioned that 
the fruits would contain fewer seeds. 
The critical judge of a good pummelo in Siam will lay more 
stress upon what he calls the kao sarn, or raw-rice, condition 
of the fruit than upon seediness. There is a tendency in im- 
perfect fruit for juice sacs to harden. These are not only un- 
pleasant in the mouth but indigestible, and any fruit which 
develops this characteristic is considered inferior. Soil and 
fertilization, more than any other factors, are believed to in- 
