No. 4.] DRAINAGE. 373 



(6) Only in well aerated soil do the organisms whose activity is es- 

 sential to the formation of nitrates flourish. 



(c) Well aerated soils are favorable to the multiplication and ac- 

 tivity of numerous other beneficial micro-organisms whose activity 

 increases the productive capacity. 



(d) The living root itself can maintain a condition of healthy ac- 

 tivity only where the soil contains air as well as water. 



3. The average temperature of the soil through the growing season 

 is raised by drainage, and the growing season itself is practically 

 lengthened, because rapid growth will begin earlier in the spring and 

 continue later in the autumn. 



4. Better tillage becomes possible; a wet soil cannot be brought 

 into satisfactory tilth. 



5. The probability of injury to growing crops in periods of drought 

 is reduced. This statement may at first thought seem to be a paradox. 

 The reader may be inclined to say that it seems unreasonable that 

 damage from drought should be reduced by relieving the soil from 

 surplus water. The fact, however, is unquestioned. The effect appears 

 to be due principally to the following causes: — • 



(a) The water table being reduced, roots penetrate to levels further 

 removed from the surface and therefore retaining water more effectively 

 in periods of intense heat and drought. 



(b) The physical condition of the soil above the water table is modi- 

 fied and improved. Its capillary qualities are increased. It conducts 

 water from the great reservoir below more effectively. 



(c) The feeding rootlets range more widely and deeply and are in a 

 position, therefore, to draw moisture from a much larger soil area than 

 on undrained fields. 



6. Seeds germinate more certainly and perfectly. 



7. The probability of surface wash is reduced, for the water of heavy 

 rains and melting snows is free to settle into the soil instead of running 

 off over the surface. 



8. The sanitary conditions are improved. 



Indications of Desirability of Drainage. 

 It will be apparent to all that in all cases where, under ordinary con- 

 ditions, water stands on the surface of the ground for any length of 

 time, except of course when it may be frozen in winter, drainage is 

 essential. It will, however, prove highly beneficial in many localities 

 where it seldom or never stands at the surface. The character of the 

 natural vegetation affords clear indications. In all places where 

 sedges, rushes and water grasses flourish it is certain that drainage 

 will be beneficial. The writer advises determining the average level 

 of the water table in all cases where there is doubt. This is easily done 

 by sinking holes in various parts of the field in question. Tlie height 

 of the water in these holes indicates the level of the water table, and if 

 this, during the growing season, is found to be less than three and 



