NATURAL NITROGEN

Te Awamutu Courier, Volume 53, Issue 3822, 16 October 1936, Page 5

NATURAL NITROGEN

ACTION OF SUNLIGHT ON SOILS. It is well known that nitrogen is essential to the healthy growth of all forms of plant life; but the nitrogen must be in some assimilable form, such as nitrogen compounds or ammonium salts, otherwise nitrogen starvation ensues and the plant becomes yellow and stunted. Whereever intensive cutivation is practised it is necessary to make good the steady loss of soil nitrogen by adding sewage, the ancient practice, or nitrogenous fertilisers, the modern way. The peculiar fact stands out that the plant in general is wholly unable to utilise the atmospheric nitrogenous fertilisers, the modern way. The peculiar fact stands out that the plant in general is wholly unable to use the atmospheric nitrogen that everywhere surrounds it, and which, in fact, constitutes 80 per cent, of the air, and hence, to use that pitiful modern phrase, “fl starves in the midst of plenty.” Al best only about .009002 of the atmo spheric nitrogen is actually in circulation among plants and animals. As the plant is so helpless in this respect, nature has come to its rescue by providing bacteria in the soil which are able on a limited scale to convert atmospheric nitrogen into a form useful to the plant. For example, it has been known for hundreds of years that leguminous plants, such as peas, beans, clover and lucerne, are able to look after their own nitrogen supply, while other plants are helpless. The explanation lies in the fact that the nodules or tubercles found on the roots of legumes are crowded with certain types of bacteria which convert atmospheric nitrogen into useful compounds and hand them over to the plant. Such a symbiotic, or mutual benefit, arrangement is rather limited m plant life, although it is by no means uncommon in nature. As an extreme, but not unrelated, case, one might instance the bacteria carried in the body of whales, which convert dissolved nitrogen into harmless compounds, and thus surve to protect their huge hosts from the unpleasant effects of “diver’s paralysis.” In general, however, mosf bacteria do not pay for their upkeep in such a commendable manner. ENDLESS ACTION. While symbiotic bacteria in plant life are limited to legumes, there are other “free-living” organisms which are more generally distributed, and which carry on an organised process of nitrogen fixation, slowly bringing about a general recovery in all depleted soils. This natural biochemical action goes on silently and endlessly, and in the aggregate fixes vastly more nitrogen than all the great modern chemical installations designed for the same purpose. It proceeds so slowly, however, that it signally fails to keep up with modern demands on the soil, and hence man is forced to come to the aid of the plant and supply it with the necessary nitrogen fertilisers, which, by the way, are nowadays obtained directly from the air. Free-living bacteria, such as Azotobacter, we to be found in any ordinary garden soil, and, as is to be expected, they thrive particularly well in animal manures. Experiments made with cultures of these organisms reveal that they, like all ofcher bacteria, need some energy-produc-ing food in order that they may live, grow and multiply.. In this respect, they are particularly partial to sugars, such as glucose and mannose, but a diet over-rich in carbohydrates has a harmful effect, since most of the nitrogen then becomes fixed as microbial protoplasm, or, if you like, the bacteria becomes fat and lazy. USE OF MOLASSES.

That brings us to the chief point of this article. Word now comes from India that the application of carbohydrates in the form of molasses seems to have an entirely different effect on the soil; and that perhaps too much emphasis has been laid on the nitrification by bacteria, or rather, that the attention paid to this action has obscured a purely photochemical action which probably plays an equally important part in nitrogen fixation, and which so far has been completely overlooked. Professor Dhar, a well-known Indian authority, has produced evidence which, on the face of it, seems indisputable, that the application of molasses to infertile alkaline soils has resulted in a nitrification which is not only far greater than could possibly be, expected, but which cannot be explained by purely bacterial action. He argues that the important transformation is not due to bacteria at all, but is directly attributable to a photo-chemical action whereby the nitrogen is fixed by a chemical process, promoted or accelerated by sunlight. MATTER SUMMARISED. In a recent letter to “Nature,” Professor Dhar summarises the matter in these words:—,“l am glad to inform you that molasses is being utilised in many parts of India for reclamation of alkaline land. The Mysore Government has been able to obtain 1200-1803 lb of rice grain per acre of alkaline land, using one ton

of molasses per acre on plots where crops failed previously. The normal production of rice in India is 1250 lb of grain per acre in ordinary fields. In recent publications we have shown that the ammoniacal and total nitrogen or ordinary soils mixed witn cane sugar or glucose or any other energy-rich compound, and exposed to sunlight, increase considerably, although the Azotobacter counts do not change appreciably. In the dark, however, the Azotobacter counts are enormously increased, although the ammoniacal and total nitrogen are less than in light. Moreover, we have obtained results showing the accelerating influence of light on ammonification, nitrification and denitrification under aerobic conditions. Hence we have come to the conclusion that sunlight plays an important role in the nitrogen cycle in the soil.” SOMETHING OF A REVOLUTION. In the vegetable kingdom it has always been recognised that sunlight plays a leading part in the photosynthesis of important plant products in the leaf of the plant; the claim that light plays a corresponding part within the soil, if substantiated, must effect something of a revolution in agricultural practice. Perhaps this statement should be restricted to tropical counties, since the effect cannot be so important in temperate regions owing to the lack of warmth and sunlight. In fact, this may explain why the matter has been so long overlooked. One of the greatest economic problems in, India is the reclamation of some millions of acres of infertile alkaline land, notoriously deficient in nitrogen. Moreover, half a million tons of molasses from the sugar industry is annually wasted in that country. On putting these facts together one may gauge something >f the importance to tropical India of Professor Dhar’s discovery. The progressive results of this work will be watched with considerable interest by many agriculturists throughout the world, and it may be that they will ultimately find application in tropical Australia.