8 



of nitrification during a trying time of drought. The addition of dung 

 and bulky organic manures greatly promote the water-holding proper- 

 ties of a soil, and the constant preservation of a loose surface tilth by 

 the use of cultural implements prevents the free escap ■• of soil-moisture 

 into the air. It is clear that, after all, the water supply is a most cru- 

 cial 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. 



E. — Tempera iurfi 

 The most favourable temperature for nitrification is about 100°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 Waring- 

 ton suggests, in an average English wititer the change is generally 

 going on to a small extent. In tropical climates which combine abun- 

 dance of moisture with a brisk heat, great intensity of nitrification is 

 assured and this is one of the explanations of the remarkable luxuri- 

 ance of tropical vegetation. 



N'trification goes on both night and day in the soil, and the great 

 advantage of warm nights in promoting this fermentation suggests an 

 adequate explanation of the favourable effect of such conditions on 

 vegetation. 



The temperature of the soil is obviously a question of climate and 

 season, although cultivati n can modify it to a certain extent. Efficient 

 drainage and good surface culiivation, each conduce to an economy of 

 the heat of the soil, and thereby induce improved nitrification on this 

 account. 



F. — Cultivation. 

 Although nitrifying organisms are apparently ubiquitous, 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 power. From the peculiar na- 

 tural properties of the nitrobacter orgimisms, 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 Schloe- 

 sing as to the rate of nitrification in soil under various conditions of 

 cultivation favuur this idea. 



G. — Potash and Phosphates. 

 Both types of nitrifying bacteria require a general mixed diet of 

 mineral food, b; sides 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 

 ammonia exercises a very impottant secondary action. 



Conclusions. 



(1) Sulphate of ammonia when applied 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 humus and clay. 



(3) Ammonia is converted first into nitrite and finally into nitrate 



of lime by two distinct types of bacteria. 



