SOILS 99 



warmer than the light colored ones. Southern and western 

 slopes are warmer than northern and eastern. Water logged 

 soil is colder than a dry soil. Soil well aerated by tillage, 

 drainage, and organic content is warmer than the close, dead 

 soil. 



Active organic matter in the soil. By active organic mat- 

 ter we mean plant and animal substances in process of active 

 decay. This is sometimes called humus, but we should under- 

 stand humus to mean that organic matter which is in various 

 stages of active decay from the more active stages to the car- 

 bonized inactive organic matter, such as coal. The decom- 

 position of organic matter is carried on by various bacteria 

 living and reproducing under favorable conditions upon the 

 organic matter. Such organic matter, having larger surface 

 than inorganic matter, increases the water content of the 

 soil, provides aeration and makes the soil friable. The 

 farmer may control the organic content of the soil, and this 

 control is often the beginning of soil improvement and sys- 

 tems of permanent agriculture. He may incorporate in the 

 soil the crop residues, all the animal manures available, and 

 return to the soil most of the legume crops. These practices 

 are all part of a good system of crop rotation. 



Tillage of the soil. By tillage of the soil we mean all 

 the handling of the soil usually included in the use of imple- 

 ments for plowing and preparation for plant growth. Til- 

 lage of the soil pulverizes it, and puts it into better physical 

 condition for providing itself with the proper moisture. Soil 

 that is too wet works at a disadvantage, as every farmer 

 knows, causing an injury requiring a long time to correct 



