SOIL MOISTURE AND DRY FARMING 85 



the soil, hence the great benefit of plant growth by main- 

 taining as far as this may be possible a suitable degree 

 of tilth in soils. The rootlets cannot readily penetrate 

 compact soils. The food thus absorbed is carried up 

 from cell to cell in the plants to the leaves, where it is 

 elaborated into food suitable for the plants. It is then 

 distributed to those portions of the plants that are in 

 need of it to enable them to make further growth. 



It is evident, therefore, that if plants are to be main- 

 tained in vigorous growth, the food thus carried in solu- 

 tion must be present in sufficient supply. The growth 

 made will be restricted, other things being equal, in 

 proportion as the necessary food is lacking. If not sup- 

 plied in sufficent degree to continue growth, the cells 

 become impaired and the leaves wilt. When this hap- 

 pens, growth subsequently in many instances cannot be 

 secured, and if secured it is never so vigorous again. 

 Any period of stagnation in the growth of the plant 

 hinders future development. In order to sustain good 

 growth the food in the soil must first be held in solution 

 by the capillary water in the same, hence the transcendent 

 importance of a sufficiency of this element in dry areas. 



How soil moisture may be lost. It may be lost : (1) 

 by evaporation at the surface ; (2) by transpiration 

 through plant growth, and (3) by leaching out through 

 the subsoil. These influences may operate singly at dif- 

 ferent times, or they may all operate at one and the 

 same time. The first is operative chiefly in the season 

 of mild and warm weather and the second only during 

 the growing period. The third may be operative at any 

 time, but under some conditions in dry areas it is not 

 operative at all at any time. The greatest loss, how- 

 ever, in much of the dry area, especially where the soil 

 has not been tilled, occurs in the run off water that does 

 not enter the soil at all. 



