NITRIFICATION IN THE SOIL.

Otago Witness, 14 December 1893, Page 8

NITRIFICATION IN THE SOIL.

By W. H. W.

Professor Storer, iv his recent work, bag some interesting chapters on " Nitrification and Symbiosis." This knowledge is usually locked up in scientific books away from the ordinary reader ; and the agriculturist, for whom the information is really intended, is unable to gain any benefit unless he has had a certain amount of scientific education. To bring the subject within reach of the unscientific I have prepared the following notes, principally from Sborer's Agriculture :—: —

All plants require ammonia, nitrates, or other nitrogenous substances in the soil for their proper growth. Some plants seem to thrive best on the nitrates, while other require some other material from which to take their nitrogen. When a sufficient supply of nitrogen is obtainable the leaves of the plants are of an intense green, and they are yellowish if they have not sufficient.

The decay of plants and animals is the chief source of nitrogen in the soil. But although these substances unuergo decomposition, the process is frequently not a pure chemical one — decomposition being often assisted (perhaps always) by a microscopic organism. There may be many different sorts of tbe c organisms, bub they are grouped together in the present state of our knowledge under tbe name bacteria. Some of these exist free in the soil ; others attach themselves to the plaufc. These are called parasite?, but it ia not known yet, I think, whether they are vegetable or animal.

Some varieties ot these parasites have been found attached to the roots of trees, and ifc is believed that they are nf-cecsary for the growth and development of the tree — that is, that they supply it with nitrogenous food . One peculiar thing about these trees is that the roots avo almost, if not quite, debtitu f e ot root-hairs, showing that the trees aro able to draw nourishment through the parasites from tho soil.

On the roots of plants of the poa family, such as clovers, little lumps have been noticed ;

and on examination through the microscope have been found to contain bacteria. At first they were believed to be a disease pure and simple, but they are now regarded as necessary for the proper growth of the plant— in fact, as "reservoirs of plant food." These bacteria probably take part of their food from the plant, but they also have the power of taking free nitrogen from the air (four fifths of which is nitrogen) and turning it into various nitrogenous substances that are used, not only by the parasites themselves, but by the plant. Storer put this clearly thus :—": — " The practical result of the symbiotic growth is that the fungus on the clover roots takes nitrogen from the air and assimilates it in such a manner as to form fit food for the clover x^lant, which readily partakes of the food thus offered and derives great advantage from it." It has also been found that plants growing in soils containing nitrates in abundance have few nodules on the roots. It looks, therefore, as if nature had given plants the power to take their nitrogen from the air when the soil is deficient in it. As a proof that food is stored up in these nodules, Sfcorer gives analyses to show that they contain nearly seven times as much nitrogen and nearly twice as much phosphorus as the roots themselves. Most investigators are certain that these bacteria have the remarkable power of feeding their hosts when they are attacked, or o? assistiug nitrification in the soil when they are free. Now, if these organisms are so necessary for the proper growthand development of the plant, it becomes an important question how to cultivate the healthiest bacteria for agricultural purposes. For it will probably be found that bacteria of a sickly habit will injuriously affect the plant to which they abtach themselves. Of course I don'O say that they will do so ; for very little is known of the habits of these parasites as yet. It will also probably be found that for every variety of plant there will be a special parasite. Little is known as to the conditions affecting the growth and development of bacteria. Moisture is essential ; drought prevents their growth. The process of nitrification, which, as I have above pointed out, ia probably always effected by bacteria, is feeble below 40deg Fahr., if it does not altogether cease. — (Sborer.) It is supposed to be at its maximum about 935 eg. Fahr. Below Bft or 9ft from the surface the parasite is not found, and it is said that a strong light retards their growth. — (Sfcorer ) These are the main facts concerning these wonderful organisms, so small that they are invisible to the nakpd eye, yet endowed with such important functions.