SOIL MOISTURE 



53 



the mechanical raising of water, however, by capillary action it may be 

 assumed that the limit from which water can make its way upward lies 

 much higher than the limit accessible to the roots. All the data at my 

 command regarding moisture in the soil of the Odessa Experimental 

 field point only to one con- 

 clusion, namely, that water 

 percolating beyond the depth 

 of 40 to 50 centimeters (16 to 

 20 inches) does not return to 

 the surface except by way of 

 the roots." Briggs, Jensen 

 and McLane,23 in reporting 

 upon the results of irrigation 

 experiments in citrus groves 

 in California state that avail- 

 able soil moisture below the 

 third foot did not prevent 

 orange trees from wilting 

 when the moisture content 

 in the first 3 feet of soil fell 

 below its wilting coefficient 

 and the roots of the trees were 

 limited to the first 3 feet. 

 This is a point that must be 

 kept in mind in irrigation 

 practice for it means that 

 trees can utilize the moisture 

 supply in the volume of the 

 soil that the roots occupy, 

 but very little that percolates 

 to or stands at a lower level. 

 In other words, the tree can 

 make use of the water supply 

 at 3 or 4 or 5 or 10 feet in 

 depth only to the extent that 

 it can develop a root system 

 that penetrates to these 

 depths. 



Lateral Movement of Water in the Soil. — The lateral movement of 

 water in soils is likewise dependent largely upon texture, though the 

 amount and kinds of soluble mineral salts, the soil colloids, the organic 

 material and other factors have their influences. In open, porous soils, 

 water spreads laterally to a considerable distance and with comparative 

 rapidity. In heavy, compact soils, its lateral spread is slight and slow. 



20 



40 



50 



GO 



30 

 Days 



Fig. 3. — Rate of movement of moisture in soil 

 in horizontal open flumes. Figures in circles indi- 

 cate points at which that number of liters of water 

 had been taken up. The dotted line for flume No. 

 71 (covered) is for comparison with flume No. 70 

 (open). {After McLaughlin.^^) 



