PRESIDENT S ADDRESS. 5 



to be made use of by plants. To accomplish this latter pur])ose 

 it requires a long, slow and regular process. As already mentioned, 

 the mixing of inorganic and organic matter in the soil is generally 

 carried out by worms and various minor organisms. It is the 

 task of certain of these latter bacteria to extract nitrogen from 

 the combined form to which I have already referred and turn 

 this nitrogen into ammonia. Another set of bacteria then change 

 this ammonia into certain acids which uniting with limestone 

 and similar material is turned into nitrites. Another set of 

 bacteria again convert these nitrites into nitrates which being 

 soluble in water are fit for plants to imbibe. In order to do their 

 work properly these bacteria require a reasonable amount of heat, 

 of moisture and of air, and if these are supplied all goes smoothly. 

 If. however, there hap]iens to be too much moisture whereby 

 the air becomes excluded from the ground, another set of bacteria 

 go to work and reverse all that has been done by the first-mentioned 

 bacteria and eventually the work of the destructive bacteria sets 

 free the nitrogen in a gaseoiis form and it is lost to the soil. Loss 

 of nitrogen can also take place by having the conditions too 

 favourable for the good bacteria, and if such is the case they produce 

 the nitrates in such large quantities that they cannot be consumed 

 sufficiently fast by the plants and the result is that these nitrates, 

 being soluble in water, easily get washed away and are lost. It 

 is therefore necessary to keep the soil only sufficiently loose and 

 porous to allow the beneficial bacteria to work steaclilv at such 

 a rate as not to either under or over produce. I have already 

 mentioned that leguminous plants such as peas, beans, clovers, 

 lucerne, earth nuts, etc., have a means by which they can take 

 in their necessary supply of nitrogen from the air. This they 

 do not, however, do direct from the air as is done by plant life in 

 general in the case of carbonic acid. It is done in the following 

 manner. There are again a certain kind of bacteria which attack 

 the roots of these particular leguminous plants and these particular 

 bacteria themselves absorb the nitrogen from the air and make 

 it available to be consumed by the roots of the plants they are 

 actually living on. These bacteria are present in most oi' our 

 soils, and though experiments have been made here and elsewhere 

 to increase their number by inoculation of the soil with nitro- 

 bacterine, it is doubtful whether it has done much good. The 

 roots therefore of leguminous plants when left in the ground after 

 reaping have with them these little colonies of nitrogen bacteria 

 and by this means a fresh supply of nitrogen is deposited in the 

 soil. It is now a common practice to specially grow leguminous 

 crops and then plough them in when green and in this way still 

 further increase the store of nitrogen in the soil. Though I have 

 said that leguminous plants draw their nitrogen in the manner I 

 have described above, yet if there should happen to be a good 

 proportion and in a form suitable to the plants there is no doubt 

 that these plants would also draw largely from the source of supply 

 in the soil as do other plants. Leguminous crops should preferably 

 be grown in soils which are not suitable for non-leguminous crops, 

 and where these crops are grown and ploughed in, a land which 



