Relation of Soils to Moisture and Air 55 



The advantages of underdrains over open ditches are so 

 many that the matter is hardly debatable. Underdrain- 

 age, by lowering the standing water in the soil, admits the 

 air to a greater depth and hence tends to make the soil 

 warmer. It improves the mechanical texture of the soil 

 through this admission of air separating the soil particles. 

 The roots of plants are able to run deeper into the soil by 

 reason of the improved depth of aerated soil and the im- 

 proved texture. The soil dries earlier in the spring, and 

 hence can be worked at an earlier date, which is of itself 

 advantage enough to pay for the work. The presence of 

 standing water in the soil prevents the release of nitrogen 

 from the organic matter in the soil in the form of nitrates 

 for the use of plants, both by shutting out the air and by 

 preventing the increase of the bacteria which are engaged 

 in the process of the nitrification or change of organic 

 nitrogen to nitrates soluble in the soil water. There is also 

 an acid condition in wet soils that is unfavorable to the 

 growth of plants, and particularly unfavorable to the life 

 of the soil bacteria, the microscopic plants which, as v/e have 

 seen, are among the most important of the agencies engaged 

 in the production of the higher plants that form our crops. 

 The immense arid regions of the far West, 

 Irrigation— ^j^^j.^ ^-^e rainfall is too light for the pro- 

 Surface and , . - 1 . .. 

 Overhead duction of crops, are made m many sections 



extremely productive through irrigation from 

 canals conveying the water at a higher level from the upper 

 waters of the streams. The United States Government is 

 now engaged in a vast system of storage lakes in this region 

 so that great areas of the land now in desert by reason 

 of lack of rainfall, will be brought into cultivation. The 



