SCIENTIFIC AGRICULTURE. 181 



there is little organic matter present, this practice is injurious. 

 The process of burning, according to Boussingault, ought to 

 cease after the organic matters are reduced to a blackish ash ; 

 for when carried beyond this, so that incineration is complete 

 and a red ash is left, it may materially injure, if not render 

 the soil barren. 



DRAINING. 



The draining of wet lands has become one of the most im- 

 portant branches of mechanical agriculture. An excess of 

 water in the soil prevents the access of air, reduces the tem- 

 perature, favors the formation of frost, fogs and mildew, and 

 renders tillage difficult or impossible. Soils may be rendered 

 too wet in various ways, as, by the tides of the sea, by the 

 setting back of rivers, by permanent springs in the soil, by 

 small subterranean streams, and by the compact and retentive 

 nature of the soil or subsoil. The advantages of draining, and 

 the various modes by which it is best accomplished, are well 

 described by Johnston and Colman, from whose works the fol- 

 lowing facts in relation to the operation are derived. 



1. It carries off all stagnant water, and gives a ready escape 

 to the excess of what falls in rain. 2. It prevents the ascent 

 of water from below, either by capillary attraction, or springs. 

 3. It allows the water of rains to penetrate, and find a ready 

 passage from the soil, instead of washing the surface. 4. The 

 descent of water through the soil is followed by fresh air, which 

 occupies the space just left by the water. 5. The soil after 

 thorough draining becomes looser, more friable and easily 

 broken ; this is especially true of stubborn clays, which in 

 practice become altogether another soil. 6. By freeing the 

 soil from the excess of water, it becomes warmer, and thereby 

 advances the crop to an earlier harvest: thus it is "equivalent 

 to a change of climate" 7. When the autumn is wet, drain- 

 ing carries off the superabundance of water, and prepares the 

 land for sowing fall crops, which would otherwise be retarded, 



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