88 REPORT OF THE AGRICULTURAL RESEARCH INSTITUTE 



It is not clear at present whether this is due to the forma- 

 tion and reduction of nitrates or to incomplete oxidation 

 consequent on the lack of activity or insufficient number of 

 nitrate formers in the soil. Evidence is not wanting that 

 in many of the soils examined the very slow rate of nitrifi- 

 cation observed under optimal conditions of aeration and 

 water content, is due to the absence in sufficient numbers or 

 lack of physiological activity of the necessary nitrifying 

 organisms. It will be readily realized what an important 

 field for enquiry is opened up by this observation, which,, 

 however, in view of its wide divergence from received ideas 

 on this subject, will require further substantiation by care- 

 ful experiment and observation. The effect of nitrites on 

 seedlings and the concentration required to produce the pre- 

 judicial results observed, was ascertained for various field 

 crops in water culture. At the same time observations were 

 made as to the concentration of nitrites occurring in the 

 soil water under various conditions, but in none of the soils 

 examined was this found to rise to the degree found toxic in 

 water culture. It does not necessarily follow that this stat- 

 ical treatment of the question disposes of the possible in- 

 toxication by nitrites of plants growing in such soils, owing 

 to the necessity for taking into account the constant forma- 

 tion of nitrites in the soil to replace those absorbed by the 

 plant or oxidized in the soil, and the possibility of cumula- 

 tive intoxication in the plant itself of which at present we 

 know nothing. The presence of nitrites in soil was found 

 to affect germination and early growth ; this explained the 

 apparently anomalous result of an experiment in which ger- 

 mination in a well-aerated soil compared unfavourably with 

 that in the same soil badly supplied with air; on further 

 examination it was found that in this soil when well aerated 

 complete nitrification was preceded by the incomplete stage 

 of nitrite formation and accumulation, and as this was coin- 

 cident with the germination period of the seeds sown there- 

 in the germination of the latter was interfered with to a 

 greater extent than in the soil in which no nitrification was 

 taking place. 



