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THE AGRICULTUEAL NEWS. 



Mauch 26, 1904. 



NOTES ON NITRIFICATION. 



Mr. H. H. Coiisin.«, M.A., F.C.S., writes in the 

 Bi'Uet'in of the Jumtiini Dcpartwrvt of Affrividfare 

 for January on the stihject of nitrification. We reprint 

 the following notes relating to the conditions affecting 

 the nitrification of ammonia : — 



rEESEXCK or ORGANISMS. 



Fortunately for the ngrii-nlturist, the liactevia responsible 

 foi- nitrification are vnivfrfnUi/ diftri''ii'al and no practical 

 cultivator runs risk of loss t'hrongh the actual absence of 

 nitrifying organisms. Cultivated soils from all .source>, 

 desert sand and rocky fragments from lofty mountain tops, 

 have all yielded proof of the presence of nitrifying bacteria. 

 ■\Varington found that all the samples taken from the 

 cultivated surface of the soil vhich he tested contained 

 nitrifying organisms. At a dejith of 2 feet, powers of 

 iiitrilication were occasionally lucking, while at a depth of 

 C feet and over the soil had lost all such powers. Nitrifying 

 organisms, therefore, are mainly i)resent in flie upper iiUciJ 

 surface of the soil and do not e.xist in the lower depths of 

 unstirred soil. Such a distribution is obviously due to the 

 fact that conditions favc>urable for nitrification are alone 

 possible in the upper surface of the soil. 



AIK. 



The atmosphere contains one-fifth of its volume of 

 oxygen gas and as this latter material is requisite for 

 the purpose of oxidizing ammonia, a full supply of air is 

 necessary for the free progress of the change. iJrainage. 

 cultivation with iilough and harrow, spade, fork and hoe are 

 time-honoured tributes to this fundamental requirement of 

 cultivated ground. A water-logged soil, in which tlie pores 

 are saturated with water, is an impossilile medium for 

 nitrification owing to the absence of air. The wonderful 

 improvements that ha\e been lirought about in the case of 

 .stiff, impervious soils, bj- drainage and good cultivation are 

 closely associated with the improved aeration of the soil and 

 the consequent promotion of nitrification. 



PKESENXE OF SALIFIABLE BASE. 



It is desirable that special emphasis be laid on the 

 absolute necessity of such an alkaline carbonate as chalk 

 for the general requirements of the ]irogress of nitrification. 

 Those traditions of good cultivation which have been evolved 

 through centuries of experience and observation by 

 generations of practical men, have received marked confirma- 

 tion and a rational explanation through the latest discoveries 

 as to the causes and conditions of nitrification. The 

 recommendations c>f science, based ui>on a comprehension of 

 the cau.ses at work, are singularly in harmony with the 

 general maxims of good cultivation, based upon a shrewd 

 appreciation of obvious effects. Of all the conditions 

 favouring nitrification, lime or chalk is the one that is most 

 frequently lacking in practice and that merits the careful 

 consideration of every agriculturist who seeks to obtain the 

 best returns from the cultivation and manuring of his laud. 

 Chalk is rai)idly washed out of cultivated soil through the 

 action of water and carbonic acid, and moreover, it is an 

 essential for the working of sulphate of ammonia at twr. 

 stages of its history in the soil. 



MOISTURE. 



When soil is dust-dry, nitrification ceases. Schloesing 

 found, for instance, that provided the soil was not water 

 k>"ged and free aeration was secured, the rate of nitrification 

 increased with the proportion of moisture in the soil. 



From the jioint of view of practice, nitrification is thu.s 

 seen to have a close cfmnexion with the accidental variatior.s 

 of season, other conditions being the same. A season of 

 intermittent and fairly liberal rainfall is most favourable for 

 nitrification. Excessive wetness, however, dei>resses this 

 activity by reducing the tem|)erature of the soil and overload- 

 ing it with moisture. It is important to note that cultivatifin 

 is of great service in promoting and maintaining the jirogress 

 of nitrification during a trying time of drought. The addition 

 of dung and bulky organic manures greatly i>i'omotes tht- 

 water-hokling i>roperties of a soil, and the constant preserva- 

 tion of a loose surface tilth by the use of cultural imiileinents 

 prevents the free escape of soil-moisture into the air. It is 

 clear that, after all, the water sujiply is a ino.st crucial factor 

 in the development of our crops, for not only does this limit 

 the direct feeding capacity of the plant but also the rate of 

 production of nutritive nitrates from the humus of the soil 

 and such manures as sulphate of ammonia. 



TEMPER.^TUKE. 



The most favourable temperature for nitrification is 

 aV)OUt lOO'F., at which temperature Schloesing found it to be 

 ten times as active as at 57°F. In hard frost the action 

 entirely ceases, but, as Warington suggests, in an average 

 Engli.sh winter the change is generally going on to a small 

 extent. In trojiical climates which combine abundance of 

 moisture with a brisk heat, great intensity of nitrification is 

 assured and this is one of the exiilanations of the remarkable 

 luxuriance of tropical vegetation. 



CULTIVATION'. 



Although nitrifying organisms are ai>parently ubicpiitous, 

 their rate of reproduction is relatively slow. A reclaimed 

 soil which has been hitherto unproductive generally requires 

 one or two seasons to develop normal intensity of nitrifying 

 iiower. From the peculiar natural proi)erties of the nitro- 

 baiter organisms, it would appear that constant stirring and 

 turning of the soil .should promote their uniform distribution 

 and rapid increase in the soil, and experiments by Schloesing 

 as to the rate of nitrification in soil under various conditions 

 f.f cultivation favour this idea. 



I'OTAsH .\XD PHOSPHATES. 



I'.oth tyjies of nitrifying bacteria require a general 

 mixed diet of mineral food, besides the carbonic acid gas and 

 ammonia which form their staple nourishment. Of these 

 minerals, potash and phosphates are of the chief importance. 

 It is thus evident that a well nourished soil not only feeds 

 a crop directly, but by promoting nitrification of annnonia 

 exercises a \ery important secondary action. 



CoSCLUsIONS. 



(1) Suliiliate of ammonia when ajiplied to fertile .soil 



gives up its acid to the chalk with which it comes 

 in contact. 



(2) The ammonia is then absorbed by the soil and 



prevented from loss by drainage owing to the 

 guardianship of hunuis and clay. 



<:'<) Ammonia is converted first into nitrite and finally 

 into nitrate of lime by two distinct types of bacteria. 



(■f) The general conditions of soil-fertility are closely 

 connected with those of nitrification : good cultiva- 

 tion promotes efficient nitrification. 



(.")) The rate of nitrification of ammonia corresponds 

 with the requirements of jilants, and during the 

 growing season this change takes jilace quite as 

 fast as is gnod for the plant. 



