90 ELEMENTAKY AGRICULTUKE 



Then, as we have said, there are the hosts of soil 

 bacteria whose work it is to change certain plant 

 foods for the plant's use; and these bacteria can not 

 live without air. 



How to Drain Swampy Land. Level fields of clay 

 soil are often unfit for crops, because they do not 

 drain well. They are always water- soaked and 

 swampy. Thus the farmer must drain such fields 

 or allow them to lie idle. The best method is to 

 tile-drain them. This is done by digging trenches 

 from thirty to one hundred feet apart, according to 

 the soil. In the bottom of these trenches tiles are 

 laid. These tiles are merely hollow tubes about a 

 foot long, made of clay and burnt hard like brick. 

 They are laid end to end about four feet below the 

 surface of the ground. Care must be taken to see 

 that the tile line slopes gradually to some lower level 

 at the creek or river. 



How Draining Helps. The tile drains carry away 

 the excess of water. This allows air to enter the 

 soil, and plant roots will follow as deep as the air 

 and so get more plant food. Bacteria can also find 

 better homes because of the air in the soil. 



A Map of the Tile Lines. The tile should not be 

 too small, as small ones get filled up easily. Noth- 

 ing smaller than three inches in diameter should be 

 used, and in many places only four-inch tile are laid. 

 Tiling a field costs a great deal of money and it 

 should be done right. A map of the field may be 

 kept showing just where every tile line is, so that 



