FIFTH ANNUAL YEAR BOOK — PART VI. 523 



cooler than the air which enters the drain and hence this air is cooled with 

 the result that the soil is moistened by the water which is deposited by the 

 air. 



In many sections of the central west serious losses frequently occur owing 

 to the heaving of grass and cereal crops. Proper drainage of the soil is 

 doubtless the most eflfective remedy for this difficulty. When soil water 

 freezes it expands; the surface soil is thus raised and the roots of the plants 

 are torn from their place of growth. Shallow rooted plants are thus left on 

 top of the ground after the surface soil has thawed and settled into position. 

 It is not an uncommon occurrence after a series of freezes and thaws, in the 

 latter part of the winter or early spriag, to find roots of clover, wheat 

 and some other crops partially or wholly exposed. The percentage of plants 

 thus destroyed in many fields in a single winter is so great that the farmer is 

 compelled to reseed the land. Soil which has been drained and is free from 

 surplus water is well supplied with interspaces filled with air. Therefore, 

 when the soil moisture freezes, abundant room is afforded for expansion and 

 thus the plant roots are protected in the largest measure from the injurious 

 results which it has been shown follow the expansion and contraction of the 

 surface of the soil. 



Again, many farmers do not appreciate the value of draining rolling land. 

 They do not understand the results which follow tilling land of this char- 

 acter. On hillsides, having a clay subsoil, the water which falls upon the 

 surface will sink mto the soil and be carried off underground instead of over 

 the surface if an underdrain has been located in the subsoil at the depth of 

 three or four feet. When these hillsides are drained this surplus water will 

 be readily carried off, with the result that the soil will not become so thor- 

 oughly saturated and surface washing will in a large measure be prevented, 

 lu' a few years this well drained land will be greatly improved by the ac- 

 cumulation of humus within the surface soil, by the circulation of the air 

 among the soil particles and by the action of the soil bacteria, which, now 

 for the first time, find within its depth a suitable and congenial home. On 

 hillsides not adequately drained the surface soil, permeable by water, is 

 very thin and is frequently underlaid by a stiff and almost imprevious clay. 

 The result is that when beating rains fall they carry more or less of this 

 surface soil into the valleys below. This action annually removes a con- 

 siderable portion of the most fertile soil and is one of the most potent factors 

 in keeping these rolling lands less productive than they would be under 

 more rational management. 



The one problem, which doubtless more than and other, is extremely 

 perplexing to the drainage engineer, is that i elating to the depth and dis- 

 tance apart of drains in the various types of soil such as sand, clay, gumbo 

 and peat. Few written statements, based upon experimental work, can be 

 found regarding the subject. Farmers and engineers have many theories 

 along this line, but after all, the fact remains that very few meo , if any, 

 are in a position to give definite recommendations regarding the drainage 

 of a given area of any of these soils which are among the most difficult to 

 drain. There are good reasons why this is true. In the first place drainage 

 work in this country has extended over a comparatively brief period of 

 time, and secondly, in few instances have records and data been kept 



