THE NEW SOIL SCIENCE. 



8B 



or nitrate of potash, and is ready for plants to absorb. This is the 

 explanation given of the way and form in which plants obtain their 

 nitrogen. 



I take it for granted that the bacteria do make nitric acid from 

 organic nitrogen, but I cannot believe that this is the only product formed. 

 Of what are their own bodies composed, small as they be ? And if they 

 are not actually soluble in water, they are so transparent as to be incapable 

 of discolouring water even when there are millions present. 



Is it not possible that in the formation of nitric acid some soluble 

 organic compound is formed, which is absorbed and utilised as food by 

 growing crops ? Or may there not be present in soils microbes making an 

 organic compound which is so used? 



The compound may be, and no doubt is, a complex substance contain- 

 ing in addition to nitrogen some or all of the other elements of plant food 

 such as potash, sulphur, phosphorus, magnesia, Sec. This supposition 

 may at first sight be thought incorrect, but why do we find it necessary to 

 apply to soil phosphates and the other elements of plant food to supply 

 the bacteria with the constituents necessary for their development if they 

 are not utilised by them ? 



Professor Aikman says in his book ''Manures and Manuring : " "In 

 experiments on nitrification it has been found that the organisms will not 

 develop in any medium destitute of phosphoric acid. Probably potash, 

 magnesia, and lime salts are necessary. In the cultivating solutions used 

 in the experiments on the subject the mineral food constituents added 

 consist of lime, magnesia, potash salts, and phosphoric acid." If these 

 things are necessary the bacteria must use them, and if used they must 

 either be made into some organic compound or go to form the bodies of 

 the organisms. Think of these millions of tiny microscopic bits of organic 

 matter, living, dead, and dying, constructed of material similar to that of 

 our garden plants, in close contact with their roots, and who can say that 

 they are not absorbed and used ? 



A germinating seed contains sufficient organic food to enable the 

 embryonic plant to grow and develop until large enough to provide for 

 itself. The food consists of all the elements needed for perfect growth ; 

 the nitrogen, potash, phosphoric acid, &c, are all present in an organic 

 form, and yet the plantlet feeds upon them after they are made soluble by 

 the action of ferments. 



Again, I suppose no one thinks the organic substance made by bacteria 

 in the nodules on the roots of Peas, Beans, &c. is changed into nitrates 

 before the plants use it. 



Then we have certain plants which live upon organic nitrogen from 

 the bodies of the insects they trap. 



If plants can only absorb their nitrogen as nitrates and ammonium 

 salts, whence do forest trees and bog plants get their nitrogenous food ? 

 The conditions in the forest soils and in bogs are unfavourable for 

 nitrification, and yet the trees and plants grow freely enough. 



If we take it for granted that there exist in soils bacteria whose 

 function is to produce, or make, certain organic compounds for each of 

 the different crops we grow, we could satisfactorily answer many difficult 

 problems which now trouble us. I have in my mind two which are 



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