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THE AGRICULTURAL NEWS. 



April 13, 1912. 



investigated by some workers with reference to the 

 effect produced by the addition to it of carbohydrates 

 such as starch and sugar (sucrose). Under the condi- 

 tions of the experiments, this was found to cause injury 

 to growing plants, whereby development was retarded, 

 and the roots killed to a large extent. The reason 

 adduced for this effect is that the presence of so large 

 a proportion of carbohydrates in the soil led to so great 

 an increase in ihe number of bacteria that, in the 

 competition for the available supply of air, the roots of 

 the plants suffered. This effect was hardly expected. 

 for it was considered that the increased supply of 

 carbohydrates would result in the usual increase in 

 numbers of the chief nitrogen-fixing organism — Azoto- 

 bacter — with a consequent favouring of the growth of 

 the plants. The apparently abnormal result was shown 

 later, however, to have been produced by the circum- 

 stance that the experiments were conducted during the 

 spring of the year, when the temperature of the soil 

 was such that the activity of Azotobacter was at its 

 lowest, while that of other bacteria, notably those of 

 putrefaction, was much greater. On repeating the 

 trials, in autumn, the nitrogen-fixing organism took 

 advantage of the greater supply of the carbohydrate 

 required for providing it with the energy for doing its 

 work, with beneficial results to the succeeding crop 

 Trials of a similar nature in the tropics, employing 

 molasses as the source of carbohydrate, and sugar-cane 

 as the crop, have indicated beneficial results in Mauri- 

 tius and possibly beneficial effects in Antigua; while in 

 British Guiana, it has been demonstrated so far that 

 the application of molasses to sugar-cane lands is not in 

 the nature of a commercial success. 



The nitrogen-fixing organism, Azotobacter, as has 

 been indicated, derives the energy needed for this 

 action by the destruction of carbohydrates: that is to 

 say by employing as sources of that energy substances 

 of the nature of starch and the sugars. It has also 

 been stated that the measure of the activity of soil 

 bacteria in laboratory experiments is not on a scale 

 affording comparison with that existing under natural 

 conditions. Thus with Azotobacter, the amount of 

 nitrogen fixed, in relation to the quantity of carbohy- 

 drate destroyed, is very small in experiments of the 

 former kind, in comparison with that indicated in trials 

 on a field scale. This condition has led to the making 

 of investigations to find a reason for it, and the result 

 has been to show that while at first the ratio of nitrogen 

 fixed to the carbohydrate used is high, even in the 

 small scale experiments, this decreases quickly, as the 

 time goes on, because, as it is explained, of the accumu- 

 lation of nitrogenous material under the conditions of 



the trials, whereby the Azotobacter is caused to use 

 the carbohydrate for purposes other than the fixation 

 of nitrogen. It is natural to conclude that this change 

 in its action on carbohydrates does not occur in the 

 open soil, because the conditions do not ordinarily 

 exist there for the concentration of the nitrogenous 

 material that is effective in causing it to take place. 



Another reason for the apparently increased 

 activity of Azotobacter in soils has been found in the 

 fact of the presence of humus, which results in the 

 stimulation of the organism owing to the fact that the 

 hamus contains small quantities of silicate of iron, and 

 similar bodies, the effect of compounds of iron being such 

 that this depends largely for its extent on the nature of 

 those compounds. As these are present in basic slag, 

 the circumstance forms an explanation of part of the 

 beneficial effect on nitrification that is known often to 

 follow the application of this manure. 



Among the bacteria that have been found to exist 



normally in soilareanumber of heat-loving organisms 



that is organisms that can thrive at temperatures 

 sufficiently high to kill the majority of other, similar 

 forms of life, as well as those more highly organized. 

 Experiments have shown that these have the power to 

 fix nitrogen at a temperature as high as 142'F. The 

 matter is suggestive in connexion with the supposition 

 that such organisms may have a larger importance unJer 

 tropical, than under temperate conditions. 



There has been no new work of a striking nature, 

 with respect to the benefit to plants of heating and 

 partially sterilizing the soil, though accounts have been 

 published by several investigators, of the effects pro 

 duced by antiseptic substances. In the case of these, 

 the improvement of the conditions, as regards jjlant pro- 

 duction, by the application of such substances to 

 the soil, has been attributed to the stimulus that they 

 are thought to give to the beneficial organisms in the 

 soil, rather than to the reason adduced bv Russell 

 and Hutchinson,* namely the destruction that they 

 cause of the larger organisms which employ the bacteria 

 as food; and this conclusion is reached notwithstanding 

 the fact that the work of these investigators was, in one 

 of its aspects, conducted for the purpose of showing 

 that the benefit arising in the soil after heating or 

 partial sterilization cannot be attributed to the direct 

 stimulation of bacterial activity. 



The circumstance that has just been mentioned, 

 namely, the effect of partly sterilizing the soil by heat 



Agricitltnral News, Vol. IX, p. .33. 



