: 67 



The results already obtained by experiment are of great value in indi- 

 cating how some of the factors on which the use of water depend can be 

 controlled by the irrigator. These results may be summarized as follows: 

 Extent of exaporation from bare soils not cultivated. 



On four California orchard soils an average of 12% inches of irrigation 

 water was applied and the evaporation loss per season (Feb. 23rd to Aug- 

 ust 31st) was 94 per cent. This shows the large percentage of loss in soil 

 moisture which may obtain during a long season. The rate of evaporation 

 depends much on the moisture in the soil. The results obtained on a sandy 

 orchard loam in southern California are as follows: 



For a sandy loam saturated weekly evaporation was 4.75 in. water 



Fora sandy loam with 17.5% free water. . . .weekly evaporation was 1.33 in. water 

 For a sandy loam with 11.9 % free water .... weekly evaporation was 1.13 in. water 

 For a sandy loam with 8.9 % free water .... weekly evaporation was .88 in. water 

 For a sandy loam with 4.8 % free water. . . .weekly eavporation was .25 in. water 



The large rate of evaporation from soils which are very wet indicates 

 the necessity for wetting as little of the surface as possible when irrigating. 

 With orchards this may be obtained by using deep furrows. 



The rate of evaporation for a period of 33 days following an irrigation 

 6 inches in depth is illustrated in the diagram given below for a California 

 brown loam soil not cultivated after irrigation (Fig. 45). This diagram 

 shows the excessive rate of evaporation immediately after irrigation when 

 the surface soil is very wet. The loss during the first three days was 17 

 per cent, of the water used and is about equal to one-half of the total loss 

 during the 32 days which is 35 per cent. These results indicate the im- 

 portance of preventing the evaporation loss as early as possible after 

 irrigation. 



Effect of Depth of Furrows on Evaporation from Soil. 



Fig. 48. 



