FARMERS' INSTITUTES. 23 



magnesium and sodium nitrates are then treated with potash salt to con- 

 vert them into potassium saltpetre. 



In the manure heap and in the soil there is a process diametrically 

 opposed to the preceding. Instead of nitrogen being rendered avail- 

 able to plant growth it becomes lost for immediate purposes. 



The liberation of nitrogen and the denitrification of organic matter 

 appeals to the farmer as an important economic problem. Attempts 

 have been made to reduce this peculiar action to the minimum by 

 various means. 



In the decomposition of proteid material there is always considerable 

 less of nitrogen through the evolution of ammonia gas. Many bacteria 

 have this power of acting upon nitrogenous material and producing 

 ammonia. From the ordinary manure heap it is no diflScult matter to 

 separate several varieties belonging to this type. The ammonia escapes 

 into the air and is consequently lost for direct fertilizing purposes. The 

 manure has consequently^ lost so much in value. 



Several species of bacteria have been found which are capable of pro- 

 ducing free nitrogen. This, however, results from certain bacteria upon 

 the nitrates already formed and do not act so much upon the proteid 

 substances. With sufficient food some of these germs seem to possess 

 no limit of action, and again there are some which possess this property 

 to a very marked degree incapable of changing nitrates to free nitrogen 

 unless associated with some other bacterium. The potassium or sodium 

 present in the form of a nitrate is converted into a hydroxide and 

 eventually change the medium in which the germs are growing into 

 a condition inhihitive of life. The process may go on in many instances 

 either in the presence of or absence of air. It becomes possible there- 

 fore for denitrification to take place either on the surface or deep in the 

 soil. 



These bacteria are present in the excreta of animals and especially 

 the dung of horses. So great is the loss that it is claimed from actual 

 experiment that onlj' twenty-five per cent of ammonia is recovered in the 

 plants. 



In the transformations produced by this class of bacteria, there some- 

 times occurs a combination of nitrogen which in reaction with ammonia 

 yields free nitrogen. This method differs somewhat from that of simple 

 reduction of the nitrates. 



What waste takes place by the growth and function of these bacteria 

 it is not easy to determine, but it must be vast, inasmuch as it is likely 

 to occur in all manure and all fertile soils possessing nitrates. 



After discussing the value of the nitrifying bacteria and the loss 

 accruing from denitrifying bacteria, it may be interesting and helpful 

 to consider briefly that class of bacteria which abstract free nitrogen 

 from the air for the utilization of plants. 



It has been well known for a great many years that if seeds of 

 leguminous plants were placed in a soil with all the necessary ingred- 

 ients except nitrogen they v/ould start their growth, and as soon as the 

 food provided by the seeds was gone they would undergo a sort of with- 

 ering process known as nitrogen-hunger for a time and then begin to 

 resuscitate themselves. Most plants not belonging to the leguminosae 

 withered away and finally died. Peculiar enough also was the fact that 

 these leguminous plants and others following in the same category con- 



