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. 



(3) 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 labor 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. 



