700 SOILS: PROPERTIES AND MANAGEMENT 



that grow in standing water, such as rice and cmn- 

 berries. 

 Its disadvantages are : — 



1. A large quantity of water is required. 



2. Over irrigation, with consequent seepage and diffi- 

 culties from alkali, is likely to occur. 



3. On heavy soil, puddling and checking of the surface 

 soil result from lack of tillage. 



4. Some crops are injured by direct contact with water. 



5. The cost of leveling and of construction of levees is 

 large. 



There are two main types of flooding. In the first 

 the water is turned into level checks or blocks, where 

 it stands until it is absorbed by the soil — called commonly 

 closed-field flooding. In the second type the water is 

 distributed in a moving sheet or a series of small rills, 

 from field supply ditches — called open-field flooding. 

 This method is used only where there is a moderate slope 

 to carry the water. 



In closed-field, or check, flooding, the land is divided 

 into blocks, each having a level surface and surrounded 

 by a levee. The size of the checks, their shape, and the 

 height of the levees is determined by the contour of the 

 land. On a slope they may be very irregular. Small 

 checks of one to three acres are most successfully irri- 

 gated, but areas of twenty or more acres have been flooded 

 in one block. A flow of five to seven second-feet of 

 water is necessary in order to make the method thoroughly 

 successful. One man can irrigate from five to twenty 

 acres a day, depending on the size and form of the checks. 

 The levees may be permanent, as is usually the case 

 especially in meadows, or they may be thrown up for 

 each application of water. The permanent levees may 



