Dry Farming and Irrigation 169 



Another measure according to which the farmer may The acre 

 be charged for the water he uses is the " acre foot." ^ 

 The acre foot is the amount of water necessary to cover 

 one acre a foot deep. This is equal to 43,560 cubic feet. 



A way of stating the measure of water where large The 

 quantities are flowing, as in a river, is to tell the number v ^^ Te 

 of cubic feet per second passing a certain point. 



Experiments and Observations 



1. Pour water on freshly spaded ground and on uncultivated 

 ground. Notice the difference in absorption. 



2. To show that water rises in packed soil, make footprints in 

 freshly cultivated soil and notice early on the next morning that 

 the surface in the tracks is wet while the surface of the loose ground 

 is dry. 



3. Find weeds or other plants growing alone and notice how 

 much larger they are than similar plants where the stand is 

 thick. 



4. To illustrate a miner's inch, make a water-tight box and cut 

 an inch hole in one side near the bottom. Run water into it fast 

 enough to keep the water level four inches above the middle of 

 the hole (Fig. 131). 



References 



"Management of Soil to Conserve Moisture." Farmers' Bulletin 266. 

 "Practical Information for Beginners in Irrigation." Farmers' 

 Bulletin 864. 



