Moisture of the Soil. 481 



in recent writings. It is one of the most important means of 

 preventing the loss of water from the soil. It breaks off the 

 capillary pores in the soil structure and interposes between the 

 lower moist soil and the air a layer so loose that the water can 

 not rise through it. This mulch may itself dry to dust, but it 

 nevertheless protects the soil below. When soils become baked, 

 the minute capillary pores connect directly with the atmosphere 

 and the evaporation of water is very rapid. Hence it is exceed- 

 ingly important that the crust be broken after every rain. 



The hygroscopic water of the soil flows neither under the in- 

 fluence of gravity nor capillarity. It is held firmly in place 

 upon the particles of soil and can only be driven off by a high 

 degree of heat. Just how important this water is in the growth 

 of plants has not been determined, but it is probable that during 

 severe droughts it may assist in carrying the plant over, enabling 

 it to maintain itself until capillary action is restored. 



TJie necessity of water for growing plants. 



The importance of water to the growing plant can only be 

 undestood when we apprehend and appreciate how large a part 

 of its structure is composed of water, and that even this large 

 percentage of its composition is but a fraction of the total 

 amount used in its development. The quantity of water entering 

 into the structure of plants varies from sixty to as high as ninety- 

 eight per cent, of their total weight. During the entire period of 

 growth, there is a constant giving off of moisture by the foliage, 

 and it must be made good by that which is taken up by the 

 roots. By experiments conducted at the Wisconsin Experiment 

 Station, it has been found that in raising oats, for every ton of 

 dry matter produced there were required 522.4 tons of water; for 

 every ton of dry matter of flint corn there were required 233.9 

 tons of water; for dent corn, 309.8 tons of water for every ton of 

 dry matter. On plots at this Station, 1.8 tons of dry matter of 

 oats per acre represented an expenditure of 940.32 tons of water. 

 Potatoes used 422.7 tons of water per ton of dry matter. The 

 yield of potatoes on the experiment plots of 450 bushels per acre 

 during the dry season of 1895 represented an amount of water 



equal to 1310.37 tons. 



31 



