LOSSES OF MOISTURE AND PLANT FOOD BY PERCOLATION. 23 



EFFECT OF SOIL TYPE ON PERCOLATION AND EVAPORATION. 



The soils may be divided into two groups with respect to the quan- 

 tity of water which passed through them when uncultivated : (a) Those 

 whose average annual percolation is less than 10 inches, and (b) those 

 whose average annual percolation is over 10 inches. 



Table No. 6 contains a summary of percolation from the uncultivated 

 soils by groups. 



TABLE NO. 6. 

 Total Percolation in Inches from Uncultivated Soils. 



The average percolation from the clays is double the quantity from 

 the sands or sandy loams. Conversely, the sands and sandy loams lost 

 much greater quantities of water by evaporation than did the clays. 

 The above refers to the uncultivated soils. 



The average annual rainfall for the three years (December, 1913, 

 excluded) is 33.45 inches. According to the table previously cited, we 

 may expect a loss by run-off of about 8 inches on gentle slopes and 17 

 inches on steep slopes. As a portion of the Texas rainfall comes in 

 heavy rains of short duration, we may consider a loss of 8 inches by 

 run-off as a moderate estimate. 



The run-off of 8 inches is, however, less than the amount of perco- 

 lation from the sands and sandy loams. In other words, there would 

 be no percolation if we deduct this quantity of run-off. 



The percolation from the Houston loam and the clays exceeds the 

 estimated run-off by 6 inches. 



The quantity of percolating water may be assumed to represent that 

 at the disposal of the crops'. This is not strictly true, for the shade 

 and presence of the growing crop decreases evaporation from the soil; 

 while, on the other hand, a large portion of the percolation comes dur- 

 ing the winter season when there is no crop on the ground. Hence, 

 this water can be of advantage only if it remains in the soil, instead of 

 percolating. These facts must be* duly considered, and also that the 

 uncultivated soil only is being considered. The following is the crop 

 yield for which the average amounts of percolating water given above 

 would suffice, based upon the assumption that the water required is the 

 quantity given on page 6 of this Bulletin. 



