6 LAND DRAINAGE 



8. Temperature and nitrification. All the changes 

 by which organic nitrogen is put into form for use by 

 plants are accomplished chiefly by bacteria. It has been 

 found, according to Schloessing and Miintz and other 

 authorities, that these changes proceed very slowly when 

 the temperature of the soil is not higher than 54 F. 

 They proceed most rapidly when the soil temperature is 

 near 98 F. Recent research seems to indicate an opti- 

 mum temperature as low as 85 F. 



9. Nitrogen fixation. On the roots of all legu- 

 minous plants, under normal conditions, are found colonies 

 of another class of life forms, usually spoken of as bac- 

 teria, which possess the power to appropriate the free 

 nitrogen of the soil air and combine it with hydrogen and 

 oxygen to produce a form of nitrogen which the host 

 plant can and does use for food. These forms are called 

 nitrogen-fixers, and the process is sometimes called nitro- 

 gen fixation. They work most rapidly when the soil tem- 

 perature ranges from 90 to 100. These bacteria are in 

 enlargements of tissue known as nodules. 



There are probably other forms of bacteria and some 

 forms of molds in soils that have this power of nitrogen 

 fixation, and their rate of work is greatly affected by 

 temperature conditions. 



10. Temperature and germination. Most crops are 

 grown from seed. There is a temperature below which 

 seeds will not germinate. There is also, for each kind of 

 seed, a temperature at which it will germinate most 

 quickly. In Table II are shown some of the findings of 

 Sachs and Van Tiegham regarding the lowest, highest, 

 and best temperatures for the germination of the seeds 

 indicated. See also Table III. 



