Sick Soils not Influenced by Parasites 25 



Truck crops (fig. 3), grains, and fruit trees rapidly 

 deteriorate on such lands. This condition occurs in 

 a variety of soils in Colorado. It is met with in the 

 light sandy loams as well as in the heavy clay loams, 

 on lowlands as well as on hilltops. It is to be dis- 

 tinguished from true alkali troubles. 



The distinguishing characteristic of a nitre-sick 

 soil is its brownish-black wet appearance. From 

 afar the soil looks as if it had been wetted with crude 

 oil ; however the soil is usually dry. Sometimes the 

 soil may be moist and slippery, due no doubt to the 

 presence of large quantities of deliquescent salts. 

 Walking through such a field produces a sensation 

 similar to that which one would get from walking 

 on cornmeal or ashes. 



The accumulation of excessive amounts of nitrates 

 in the soil is due to the activity of a bacterial soil 

 organism, Azotobacter chroococcum. This organism 

 has the power of fixing free nitrogen from the air and 

 depositing it in the form of nitrates in the soil. The 

 conditions which favor this activity still await study. 

 Normally, soils contain from 140 to 150 pounds of 

 nitrates per acre foot. In a nitre-sick soil, each acre 

 foot contains 113,480 pounds, or 56.74 tons. With 

 such a high concentration of nitrate, it is impossible 

 for plants to grow. So far, we know of no methods 

 to reclaim nitre-sick soils. 



3. ACID-SICK SOILS 



Soils which contain an excess of acid in which 

 crops refuse to grow, may be termed acid-sick. Acids 



