156 VEGETABLE FORCING 
less with the soil preparation. An experienced grower 
states that three to five times as much water is required 
for sub-irrigation in beds that are not water-tight as with 
surface watering, and this is a serious objection when the 
supply of water is limited or expensive. 
There seems to be no difference of opinion concerning 
the advantages of sub-irrigation, which may be enumer- 
ated as follows: 
(1) The surface of the beds remains dry. This lessens 
the dangers of fungous diseases, especially of lettuce, and 
obviates the necessity of frequent tillage. 
(2) The surface of the bed remains open and porous, 
thus providing perfect soil aeration without the use of 
tillage implements. From this standpoint, sub-irrigation 
possesses special advantages for heavy soils. 
(8) Less labor is required to water the houses than 
when a hose is used. 
(4) With sub-irrigation it is possible to maintain lower 
humidity than with any form of surface watering. This 
is a special advantage in controlling certain diseases and 
in providing the most favorable atmospheric conditions 
for pollination. 
(5) The tile may be used for steam sterilization as well 
as for watering, and thus the expense avoided of special 
sterilizing equipment, and ‘the Jabor of shifting pans, 
pipes and perhaps moving the soil whenever the beds are 
sterilized. 
(6) The tile may also be used for heating the beds by 
admitting steam at low pressure. Some good results have 
been reported relating to this practice. 
(7) Sub-irrigation is the means of avoiding any me- 
chanical injury to the plants, which sometimes occurs 
when nearly mature lettuce is weighted down by water 
applied above the beds. 
(8) It is unnecessary to water so frequently when sub- 
irrigation is used. 
