FIXATION OF FREE NITROGEN 8oi 



need this element, but which are incapable of utilising it in the 

 free state in which it exists in the atmosphere. 



On poor, sandy, and gravelly soils, good crops of lupins, 

 serradella, and other leguminous plants may be grown with kainit 

 and phosphatic manures alone, and such soils are at the same 

 time so much enriched with nitrogen that they are capable of 

 yielding remunerative crops of cereals, potatoes, and other non- 

 leguminous plants. 



The amount of nitrogen-fixation which takes place when 

 nodule-bearing Leguminosae are grown on soils rich in nitrates or 

 other forms of combined nitrogen is not clearly known : the 

 nodules are generally smaller in size under such circumstances, 

 and although in many cases their number is larger on plants 

 grown in rich soil than on those produced on poor ground it is 

 by no means certain that a large number of nodules is neces- 

 sarily associated with great nitrogen-fixation under these con- 

 ditions. 



Perhaps the greatest use can be made of these nitrogen- 

 accumulating leguminous plants upon ground exhausted of 

 nitrogen and poor light soils generally, but what plants to grow, 

 how long to leave them down, whether they should be wholly 

 or partially ploughed in, or utilised for feeding purposes, and 

 many other points must be left to the future for decision. 

 However, seeing that the cost of nitrogen in a combined state 

 suitable for the nutrition of all our non-leguminous crops is 

 very considerable — generally not less than 4d. to 6d. per lb. — 

 it is essential that the farmer should consider the means here 

 at his disposal of obtaining it for nothing. 



There is little doubt that in the ordinary cropping practices 

 we do not at present take all the advantage we might of this 

 source of nitrogen, yet much investigation and experiment are 

 needed before the economic aspects of the question can be 

 fully understood. 



On land which has not previously carried any kind of legu- 



