IO4 THE SOIL SOLUTION 



conditions and denitrifying processes prevail. Warmth, moisture, 

 the reaction of the soil, and perhaps other factors markedly affect 

 the activity of the organisms of the soil solution. Another 

 important factor is that the absorptive powers of the higher 

 plants are markedly affected by sunlight, so that, especially on 

 bright and clear days, there is generally a higher concentration 

 of nitrates in the soil solution in the morning than in the evening. 

 This fact would seem to affect seriously the value of some recent 

 and extensive investigations where it has been sought to classify 

 soils by their content of water-dissolved nitrates. Nitric acid is 

 more readily leached from soils than are most other acid radicals. 

 Consequently nitrates, like other organic components of the soil 

 solution, and unlike 'inorganic components, tend to vary greatly 

 in concentration. 



