40 Subtropical Vegetable-Gardening 



tables it is sufficient to run one water furrow between 

 the rows. 



The length of the laterals for distributing the water will 

 vary with the character of the soil. In a very sandy soil 

 it is difficult to run the water for a distance of more than 

 300 to 600 feet, where the slope is about 3 inches to the 

 100 feet. Some considerable experience is necessary to 

 run the water in furrows in a sandy soil, the most important 

 consideration being that of delivering a large volume of 

 water, about 2 inches, and running it quickly down a dry 

 and well-prepared furrow. If the slope is even and the 

 soil has been well prepared, an experienced person has no 

 great difficulty in distributing the water in this way unless 

 he attempts to distribute it for more than 600 feet. 



The advantage of this form of irrigation is that it is very 

 economical of the use of water and that it has been in use 

 for many centuries and thus is familiar to many persons ; 

 its disadvantages lie in that it is applicable only to lands 

 having a proper slope and consistency, and that it requires 

 experienced laborers when used on sandy lands. 



Sub-irrigation. 



The sub-irrigation system which is also used for a drain- 

 age system during the rainy season, is one of the most 

 satisfactory that can be employed in the vegetable fields. 

 Its application is limited to lands having an even and 

 very uniform slope. One must also have an impervious 

 substratum as well as a large water supply. It is more 

 adaptable to a loamy or to a sandy soil than to a clay soil. 



The essential part of this system is a series of tile drains 

 laid out in proper conformity to the slope of the land. 



