Sl . 



I.l.GUMINOUS FORAGE CROPS 133 



formed by the joint activities of Bacillus radicicola and le- 

 guminous plants; (2) aerobic and anaerobic nitrogen-fixing 

 bacteria living in the soil itself; (3) higher plants which trans- 

 form nitrate or ammonia nitrogen, whether derived from fer- 

 tilizer or soil sources, into organic nitrogen; and, (4) a great 

 variety of soil bacteria which convert nitrate or ammonia 

 nitrogen into protein substances. This organic nitrogen is 

 made available as plant food through a process known as 

 nitrification. 1 



The steps are held generally to be two. First, the organic 

 nitrogen is changed into nitrous acid (HNO 2 ), which, com- 

 bining with calcium or some other base in the soil, forms 

 nitrites. These nitrites are then changed into nitric acid 

 (HNO 3 ), which in like manner to nitrous acid is transformed 

 into nitrates the form in which nitrogen is believed to be ab- 

 sorbed by plants. This process is attributed to the action of 

 bacteria. The first form has been given the name of nitro- 

 somonas, and the second form the name of nitrobacter by 

 Winogradsky, who has grown pure cultures of each. Under 

 certain soil conditions such as a lack of proper aeration of 

 the soil either the organic nitrogen or the nitrates of the soil 

 may be decomposed and the nitrogen set free. This process 

 is attributed to denitrifying organisms. Skilful agriculture, 

 therefore, requires that soil conditions shall be provided which 

 will assist nitrification at the proper time, prevent it at other 

 times, and prevent denitrification at all times. 



141. Effect of Lime on Legumes. It has been abundantly 

 proved that with certain soils under certain conditions the ad- 

 dition of lime may greatly increase the growth of certain 

 leguminous crops. This has been shown to be true for clover 

 at the Ohio Station and for alfalfa at the Cornell Station. It 

 has long been held that lime assists the nitrification of organic 



1 The term nitrification should be restricted to the process by which organic 

 nitrogen is changed into nitric acid, and should not be applied to the process 

 by which the free nitrogen of the air is assimilated by plants. 



