38 Practical Farming 



containing less plant food, bulk for bulk, and in a far less 

 available form, than commercial fertilizers, has a value 

 which the fertilizers do not possess. It aids in keeping up 

 the supply of humus by the decay of the organic matter 

 it contains, especially through the presence of straw, etc., 

 that has been used in the bedding of animals. The com- 

 mercial fertilizer exerts no influence in making the soil 

 more retentive of moisture, while the stable manure does 

 this essential work. The nitrogen that is in the organic 

 matter of the humus, when it is reduced to nitrates through 

 the action of the bacteria which are engaged in what we 

 call nitrification, is rapidly washed from the soil in humid 

 regions; and hence it has been shown by analysis that the 

 small amount of humus in the soils of arid regions has a 

 larger percentage of nitrogen than the larger amount of 

 humus in humid regions. 



In the soils of arid regions there is, as might be sup- 

 posed, a larger percentage of soluble plant food than in 

 the soils of humid regions, simply because it has not been 

 washed down by heavy rains. The presence of a larger 

 percentage of lime in the soils of arid regions also has a 

 tendency to flocculate the particles, and to prevent the for- 

 mation of plastic clays so common in humid sections. 

 Hence, irrigating water appHed to soils of an arid region 

 brings about a wonderful productiveness by the solution 

 of the food waiting for water. 



In the sections devoid of rainfall, Hke Peru, and parts 

 of Chin, the nitrogen has accumulated in the form of 

 nitrate of soda, which has become of great commercial 

 importance for the supplying of nitrogen to our cultivated 

 crops in the most rapidly available form. 



