Amount of Water for Single Irrigations 225 



chief loss shown in the lower three feet is due to downward 

 drainage or percolation, owing to a lowering of the ground- 

 water surface. 



The 8-foot column of fine sand, referred to above, lost water 

 by percolation in 22 hours and 46 minutes, after full saturation, 

 equal to 6.35 per cent of the dry weight of the whole column ; 

 and as this must have come almost wholly from the upper 4 

 feet, the water there must have been reduced in that time more 

 than 12 per cent, which would leave a saturation of only 8 

 per cent. 



But as plants would suffer severely for water in a soil of 

 this texture when the moisture was brought down to 4 per cent, 

 it is plain that only from 2 to 4 per cent of the weight of such 

 a soil can be added at one irrigation without entailing severe 

 loss by percolation below the depth of root-feeding. Taking a 

 cubic foot of such a soil at 105 pounds, the maximum irrigation 

 which could be applied without severe loss, supposing the ground 

 to be wet down 5 feet and the soil to have dried 3 per cent, 

 would be 15.75 pounds per square foot, or 2.86 inches in depth. 

 The sand in question, however, is more open than most agri- 

 cultural soils; hence it follows that more than 2 inches of water 

 may be safely applied at one irrigation to any crop much in 

 need of water. 



By taking samples of soil in a field of maize and clover 

 when the corn leaves were badly curled and when clover wilted 

 quite early in the forenoon, the following moisture conditions 

 were found: 



Soil moisture relations when growth is brought to a standstill 



Depth of sample 



0-6 i 11. 



6-12 " 

 12-18 " 

 18-24 " 

 24-30 " 

 40-43 " 



Clover 



PER CENT 



clay loam 8.39 



" 8.48 



reddish clay 12.42 



44 13.27 



sandy clay 13.52 



sand 9.53 



