458 THE HOME, FARM AND BUSINESS CYCLOPAEDIA. 



chanically, the crop at the time is checked in growth, and its harvest 

 yield is necessarily diminished. 



Such are a few of the evils entailed upon land by the presence of 

 stagnant water. But thorough drainage, by its negative or preventa- 

 tive action, does away with all these evils, and increases the fertility of 

 the soil. 



The positive action of drainage is very varied in its nature. It pro- 

 motes the aeration of the soil, and the circulation of rain water through its 

 pores and interstitial canals. All the openings in the soil must be filled 

 either with water or atmospheric air, and in displacing the former we in- 

 troduce the latter. Now, in addition to nitrogen, oxygen, and hydrogen, 

 of which atmospheric air principally consists, it contains carbonic acid, 

 nitric acid, carbonate of ammonia, and other gaseous compounds, intro- 

 duced into it by natural and artificial exhalations. As these ingredients 

 come into contact with the mineral matters of the soil, they change their 

 nature either by a process of oxidation and consequent reduction, or by a 

 direct union of elements so as to effect a true chemical decomposition. 

 Here is a field of tenacious land, we shall suppose, which has been lying 

 in a wet unprofitable state for a great many years. In consequence of 

 atmospheric air being excluded from its interstices, both its mineral and 

 vegetable constituents are lying in an inert useless state. But we drain 

 it effectually, and by an immediate introduction of atmospheric air into 

 the openings from which the water has been withdrawn, we set afoot a 

 series of most important chemical transformations. The vegetable mat- 

 ter absorbs oxygen from the air, and is gradually reduced to its elements. 

 Some of the mineral bodies, such as those having a considerable quantity 

 of iron in their texture, are likewise oxidized ; and instead of being any 

 longer poisonous to cultivated plants, as they formerly were, they become 

 perfectly harmless, if not even productive of good. Then, by the agency 

 of rain water and air, there are many inorganic ingredients which are 

 slowly disintegrated, and their elements fitted to take part in the building 

 up of vegetable structures. We have here a very obvious explanation how 

 it is that wet land, rich in vegetable and mineral substances, is usually 

 very productive for several years after being drained. Its constituents 

 begin at once to exert an influence on growing plants; and hence, if 

 the land be under the control of a farmer who is desirous rather to take 

 from than to give to it, he has the power of robbing it to an enormous 

 extent. 



Rain water is one of our best natural fertilizers ; and any mode of treat- 

 ing the soil, calculated to promote its percolation through its pores, must 



