THE MOISTURE IN THE SOIL 63 



plants are enabled early in their growth to send their roots down, 

 and when drought comes they are not seriously injured. Figs. 

 15-18 illustrate this. 



79a. The soil reservoir may be understood by likening it to 

 a pan. A two-inch rainfall fills an inch-deep pan and runs it 

 over ; but if the depth is increased to two inches, none of the 

 rain escapes. The hard-pan or water-table is the bottom of the 

 soil reservoir. If this bottom is within a few inches of the sur- 

 face, the ordinary rainfalls fill the soil so full that it is muddy, 

 and some of the water may be lost by surface washing. Deep 

 plowing lowers the bottom of the reservoir, and the soil holds 

 more water and yet remains drier. 



81a. Tillage operations should vary according to the nature 

 of the soil. Those soils which are loose and porous should be 

 compacted after plowing, so that the capillary connection may 

 be restored between the surface and the subsoil. The roller 

 may be used. With finely divided soils, which have a tendency 

 to become too compact, only so much tillage should be given as 

 is necessary to produce the proper degree of pulverization. It is 

 possible to so compact and fine some soils, as clays, that the 

 spaces between the soil particles is filled, and a condition is 

 produced which prevents the rise of moisture by capillarity, and 

 also prevents the absorption of rainfall and the passage of air. 



81&. Of general farm crops, about three hundred pounds ot 

 water is used in the production of one pound of dry matter. An 

 inch of rainfall weighs, approximately, one hundred and thirteen 

 and one-half tons to the acre. The student will discover that 

 the rainfall of the growing months may not be sufficient to supply 

 the crop ; hence the necessity of saving the rainfall of winter 

 and spring. 



83a. On the general subject of soil moisture and its conser- 

 vation, read Chaps, v. and vi. in King's "Soil," and Chap. iv. in 

 Roberts' "Fertility of the Land." Also consult publications of 

 the Experiment Stations and U. S. Department of Agriculture; 

 and part 3 in Vol. I of Cyclopedia of American Agriculture ; also 

 the recent soil books of Hilgard, and of Lyon and Fippin. 



