224 Nitrification in Egyptian Soils 



acre, that is, just about sufficient for the requirements of the cotton 

 crop. Owing to the long growing season of the cotton crop and the 

 active nitrification going on all the time, probably very little of this 

 nitrogen is available for the crops which follow the cotton. The nitri- 

 fication of the residues from the bersim catSi crop was followed up in 

 two cases, the land was irrigated occasionally and hoed to keep down 

 the weeds, but was otherwise not treated. 



The above results illustrate the necessity for water in keeping up 



the biological activity in these soils. The loss in nitrate indicated above 



. may possibly be accounted for by denitrification, but on the other hand 



the results are very similar to those discussed by E. J. Russell and 



A. Appleyard in their second paper^. 



Nitrification under the cotton crop. 



Observations extending over two years have been made on the 

 fluctuations in the nitrate content of the surface soil of a cotton field. 

 In 1917 a field of cotton was chosen under normal farming conditions, 

 following the winter fallow which had been studied in the preceding 

 winter. In 1918, a plot of cotton was chosen, the soil of which had 

 received no manure for some years and which, judging by the yield of 

 cereals, was in a fairly exhausted condition. The fallow period of this 

 plot was that studied in 1917-1918. 



In 1918 also, the early period of an experiment on the sowing date 

 of the cotton crop afTorded a suitable opportunity for the study of 

 biological activity in the soil as aSected by the different dates for the 

 first irrigation. 



The cotton field of 1917. 



The results obtained during 1917 are given in the following Table VII. 

 Determinations of soil nitrates were made as far as possible between 

 each irrigation period. 



The main feature of the conditions observed in 1917 is the relatively 

 high amount of nitrate present in the surface soil of the cotton field at 

 all stages of growth. The effect of irrigation in stimulating nitrification 

 is shown in the observations made about the irrigation of June 21. 



' This Journal, 8, 403. 



