117 



pipe connections from the supply tank entered directly into the 

 bottom of the soil tank instead of into an annular space. Coarse 

 gravel was spread over the bottom of the soil tank to enable water 

 to spread evenly throughout the tank area. 



Operation of Mariotte tanks does not appear as satisfactory 

 when connected to single-wall tanks as when used with the double 

 type. Some difficulty was experienced at Los Griegos in maintain- 

 ing a constant water level in tanks which apparently has not oc- 

 curred elsewhere. It appears that the reservoir of water in the 

 annular space is an advantage not found when water from the supply 

 tank is piped directly to the soil tank. There is a possibility 

 that at times water is transpired faster than it can be supplied 

 through the soil, with a resulting drop in water table. In a sin- 

 gle tank water has to pass upward through the soil column, whereas 

 in the double tank the inner tank wall may be perforated up to the 

 water table and water be supplied partly from the side as well as 

 from the bottom, thus supplying water more rapidly to the plant 

 roots. 



This investigation has confirmed results obtained elsewhere. 

 Consximptive use decreased as depth to water table increased. A 

 minimum consum.pt ive use of 10.08 inches occurred where depth to 

 water table was 37 inches, and a maximum use of 48.36 inches where 

 there was a depth of 5 inches. Between these extremes consumptive 

 use was fairly uniform. These data are presented in Table 34. 



Tules . --Consumptive use by tules in a tank surrounded by 

 swamp growth amounted to 64.68 inches for a 12-month period, or 

 83.3 per cent of evaporation from a Weather Bureau pan, a low ratio 

 compared with results of other investigations. 



