2 to SOIL CONDITIONS AND PLANT GROWTH 



and it goes on to a marked extent in wet soils. Nagaoka 

 (211, see also 7/^a) has shown that nitrate of soda frequently 

 depresses, instead of increasing, the yield of rice, sagittaria and 

 juncus on the swamp soils of Japan, an action which he 

 attributes to the formation of poisonous nitrites. Organic 

 manures or sulphate of ammonia are always used on such 

 soils, Kelley has obtained similar results in Hawaii.^ 



Denitrification will also take place in peaty soils, and this 

 has led to a very interesting observation as to the effect of 

 lime. So long as these soils are left in their natural acid state 

 nitrification cannot take place and therefore there is no denitri- 

 fication. But as soon as lime is added in sufficient quantities 

 to give a neutral reaction nitrification begins : part of the 

 nitrate is then reduced to nitrite by microbic activity, then a 

 chemical reaction sets in between the nitrite and the peat 

 whereby some nitrogen is lost and some transformed into in- 

 soluble compounds. Thus large doses of lime may produce 

 injurious effects on peat soils (Arnd (6)). 



Assimilation of Ammonia and Nitrates by Bacteria and 

 other Micro-organisms. 



Probably most of the bacteria and moulds occurring in soil 

 are capable under suitable conditions of assimilating ammonia.^ 

 The process has not been observed in ordinary arable soils 

 rather poor in organic matter; Schlosing/^;'^ (245^) recovered 

 as nitrate 98 per cent, of the added ammonium compounds, 

 so also did Russell and Hutchinson. In peaty soils, however, 

 the assimilation of added ammonia appears to be more pro- 

 nounced, amounting to nearly 30 per cent in Lemmermann's 

 experiments (170). 



Certain organisms are capable of taking up nitrates : there 

 is evidence (p. 1 79) that the action normally occurs in soils. 

 Algae would be expected to behave in this way, and certain 

 bacteria are known to do so in presence of easily decomposed 

 organic matter (38) and air, in which respect the action differs 



^ Hawaii Bull., No. 24. 



'^ Observed by Bierema {38) in 1909, and much investigated subsequently. 



