198 THE PRINCIPLES OF SOIL MANAGEMENT 



Also there is a certain inherent loss in the most careful 

 field practices, which are proportionately greater with 

 small applications of water than with large ones. It 

 has been shown (page 182) that as the capillary films 

 are reduced in thickness the movement becomes in- 

 creasingly difficult and slow. Therefore in a fine-tex- 

 tured or dense soil, where evaporation occurs only at 

 the surface, the top layer may become so dry in warm, 

 clear weather that capillary movement practically 

 ceases. Therefore, loss is also stopped. If now there 

 comes a light rainfall, sufficient to replenish the super- 

 ficial moisture films, but not enough to produce deep 

 percolation, the result may be the renewal of capillary 

 movement, which will ultimate in a few days in a greater 

 total loss than would have occurred had there been no 

 rainfall. These results have frequently been observed 

 in practice, and were definitely shown in field moisture 

 studies made by Stewart. In moisture studies of the 

 soil in the open, and under a muslin shade used in grow- 

 ing wrapper tobacco in the Connecticut valley, it was 

 observed that a small rainfall had a much larger effect 

 on the soil-moisture content outside than inside the tent. 

 A rainfall of less than half an inch increased the water 

 in the surface nine inches of the soil outside the tent to 

 a larger extent than could be accounted for by the rain- 

 fall. Careful calculations and observations indicated 

 that the difference represented movement up from the 

 subsoil, due to the renewal of film movement. King 

 has obtained similar results in field studies which he has 

 checked experimentally. This emphasizes the desira- 

 bility of storing water as deeply in the soil as is practi- 



