154 



as nitrate of soda, ammonium sulphate, dried blood, etc., is paid for at 

 he rate of from 15 to 20 cents a pound. 



HOW PLANTS GET NITROGEN FROM THE AIR. 



The air we breathe is about four-fif ihs nitrogen and one fifth oxygen. 

 We use the oxygen in breathing but discard the nitrogen. It has been, 

 regard j d merely as a material for diluting the oxygen, which would 

 be otherwise too strong for our use. All attempts to economically render 

 this nitrogen of the air available for plant food, by chemical means, 

 have been unsuccessful. Recently it has been discovered that the so- 

 call j d leguminous plants — clovers, pea?, b?ans, lupines, vetches, etc.. — 

 cm take up this nitrogen of the air, and can grow without being 

 manured with nitroge i if manured with phosphoric acid and potash. 



The manner in which this nitrogen assimilation takes place has been 

 carefully and patiently studied by scientists, and although the details 

 are not fully understood the primary cause has been found. It is be- 

 hoved that plants are enabled to get this nitrogen through the activity 

 of the lower forms of life, bacteria or microbes, which can only be seen 

 with the aid of a powerful microscope. These organism* live in the 

 soil and are to be found where leguminous plants have been grown. 

 They produce or cause the plant to produce little nodules, or tubercles, 

 on the roots It is through these tubercles that the plant gets its 

 atmospheric nitrogen. The air enters the soil by the numerous pores 

 or openings in it, which are produced by ploughing, cultivating, and 

 working the soil, by the decay of rootlets, by earthworms, etc. By 

 just what physiological processes the nitrogen assimilation takes place- 

 is a question still in dispute among scientists. It is sufficient for prac- 

 tical purposes to know that nitrogen is taken up from the air by the 

 growing plant, directly or indirectly; and that this nitrogen assimila- 

 tion takes place as a result of the life of bacteria. It is a peculiar fact 

 that few, if any, root tub >rcles are formed when leguminous plants are 

 manured with nitrogen ; the plants must first hunger for nitrogen before 

 the tubercles are formed, and the presence of tubercles indicates that 

 the plant is taking nitrogen fr>>rn the air. 



Now, curious as it may seem, there appear to be different forms of 

 bacteria for different kinds of plants. Hence it sometimes becomes 

 necessary to provide crops with the necessary bacteria before they can 

 use the nitrogen of the air. This is done by applying a light dressing of 

 soil in which the kind of plants it is wished to grow have been previously 

 grown. This is called soil inoculation. It is sometimes necessary in 

 growing a crop on a piece of land for the first time in several years. 

 Suppose, for instance, that \ eas which had been sown on land manured 

 with phosphates and potash but without nitrogen failed to grow luxu- 

 riantly. If the other conditions were favorable, the inference would be 

 that bacteria of the right kind were lacking in the soil, and a light dress- 

 ing of soil in which peas had previously been successfully grown might 

 be applied. Such treatment as this has been repeatedly tried with 

 success on a large scale. 



These discoveries throw a new light on green manuring and on the 

 plants best adapted for green Manuring. They recommend it more 

 highly than ever before as a soil renovator and a cheap means of main- 



