360 FIELD CROPS FOR THE COTTON-BELT 



and extend along one side of the area to be irrigated, or 

 in some cases completely encircle it. On each side of the 

 main canal, and running parallel with it, banks or levees 

 are thrown up which aid in holding the water. The water 

 is either pumped or siphoned into these main canals from 

 which it is distributed, through headgates or through boxes 

 put through the levee known as " trunks," to lateral 

 ditches or small canals. This system of laterals conveys 

 the water to the highest parts of the various fields. In 

 order that the water may be distributed uniformly over 

 the entire area, the fields are subdivided into smaller 

 areas. 



In the South Atlantic states, the fields are subdivided 

 by a system of small ditches or canals, a small levee being 

 thrown up on the borders of each. These ditches are usu- 

 ally parallel, about 50 feet apart, and are used for convey- 

 ing the water both to and from the land. 



In the Gulf states, low levees are thrown up on the con- 

 tour lines, usually with a plow, so as to divide the field 

 into subareas of uniform level. The water is turned 

 into the highest subarea first, from which it flows to the 

 subarea having the next highest level and so on until 

 the entire area has been flooded. 



Regardless of the system of irrigation followed, it is of 

 paramount importance that the levees bordering rivers 

 and main canals be sufficiently high to protect the rice 

 against freshets or salt water. The injury to rice from 

 freshets is due not alone to the volume of water, but also 

 to its low temperature. Salt water from the sea often 

 ascends rivers to a considerable distance, especially in peri- 

 ods of continued drought. The admittance of this salt 

 water to rice fields will destroy the crop, although slightly 

 brackish water is not destructive. 



