102 DRY-FARMING 



are some arid soils, notably gypsum soils, the par- 

 ticles of which are so uniform in size that the pore- 

 space is exceedingly small. Such soils are always 

 difficult to prepare for agricultural purposes. 



It is the pore-space in soils that permits the stor- 

 age of soil-moisture ; and it is always important 

 for the farmer so to maintain his soil that the pore- 

 space is large enough to give him the best results, 

 not only for the storage of moisture, but for the 

 growth and development of roots, and for the en- 

 trance into the soil of air, germ hfe, and other forces 

 that aid in making the soil fit for the habitation of 

 plants. This can always be best accomplished, as 

 will be shown hereafter, by deep plowing, when the 

 soil is not too wet, the exposure of the plowed soil 

 to the elements, the frequent cultivation of the soil 

 through the growing season, and the admixture of 

 organic matter. The natural soil structure at 

 depths not reached by the plow evidently cannot be 

 vitally changed by the farmer. 



Hygroscopic soil-water 



Under normal conditions, a certain amount of 

 water is always found in all things occurring naturally, 

 soils included. Chnging to every tree, stone, or ani- 

 mal tissue is a small quantity of moisture varying 

 with the temperature, the amount of water in the 

 air, and with other well-known factors. It is impos- 



