LAYING THE TILES 17 



operations. Some soils absorb and retain moisture readily 

 while others do not. Even in sub-irrigation in the greenhouse 

 beds, where we have studied this subject most, we found that 

 some soils although carefully prepared for the indoor beds, 

 were slow to absorb moisture through capillarity unless the 

 beds in which they were placed were water-tight. Some green- 

 house soils need watering daily ; others, such as those of mucky 

 consistency, need it but rarely. 



Where sub-irrigation will work well out of doors it is an 

 ideal method of watering. Some of the points in favor of it 

 are as follows : 



1. The surface soil never bakes or surface hardens. 



2. Plants run very evenly. 



3. The soil can be worked at any time and thus be kept in 

 better condition. 



4- It is claimed that less water is required. 



5. The pipes or tiles serve both to water the beds and retain 

 the excess of moisture. 



6. The openings underneath the soil allow free access of air ; 

 hence soil never becomes sour or stagnant. 



7. Surface evaporation is slight. 



8. Fungous diseases are not so prevalent. 



LAYING THE TILES FOR SUB-IRRIGATION 



Laying the tiles for sub-irrigation necessitates a knowledge 

 of many of the points already considered. On very rolling 

 ground it is necessary to follow the contour of the slopes, giving 

 the tiles a drop of about one inch in one hundred feet if in long 

 runs, or if in shorter lengths a slighter grade (see Fig. 5). The 

 distance between the rows of tile varies with the nature of the 

 soil and sub-soil, depth laid, and kind of crop to be grown. 

 Usually tiles are placed from 6^ to 40 feet apart, depending 

 upon whether they are to be used for the vegetable and flower 

 garden or for the orchard and farm. The depth generally 

 recommended is from any distance below the reach of the plow 

 to two feet below the surface. When the proper excavations 

 have been made, the same methods are employed as in deter- 

 mining the proper level for ordinary tile drainage. One must 



