J. A. Prescott 235 



These results would indicate that the root activities of a growing 

 crop have some limiting effect on the production of nitrate in the soil. 

 In both cases the fallow pots have accumulated appreciably more 

 nitrate than have the cropped pots. The difference between the results 

 obtained with maize by Lyon and Bizell and those reported above is 

 probably to be explained by the fact that in the United States the 

 maize crop is given much more space than is usually the case in Egypt. 

 The nuiize plants in the pots were certainly overcrowded. 



Sampling and determinations. 



The plots to be investigated wore sampled with a soil borer to a 

 depth of 25 cm. in at least four places and the sample brought to 

 laboratory immediately. Duplicate lots of 250 gm. each were dried 

 at 55° C. as in the Rothamsted method and the nitrates washed out 

 on a Buchner funnel with distilled water. The reduction to anmionia 

 was carried out in alkaline solution with Devarda alloy or preferably 

 by means of a mixture of zinc dust and reduced iron. 



CONCLU.SION.S AND SUMMARY. 



An attempt has been made to determine the intensity of the biological 

 processes in the soil during the most important periods of the Egyptian 

 farm rotation. The fluctuations of the nitrate content in the surface 

 soil have been taken as the most important inde.x of this activity. 



In all cases the moisture content of the soil limited these processes 

 more than any other factor. 



There was observed throughout the season in a cotton field a relatively 

 large amount of nitrate, more than sufficient for the immediate needs 

 of the cotton plant. The lack of response on the part of the Egyptian 

 cotton crop to nitrogenous fertilisers may be accounted for in part, if 

 not entirely, by the fact that nitrification in the soil is well ahead of the 

 needs of the crop. 



Nitrification under wheat and maize shows in general the same 

 characteristics in Egypt as in other parts of the world; there is no 

 accumulation of nitrate in the soil. 



The winter fallow, depending for its water on the rainfall, may be 

 a period of steady nitrification when the amount of the rainfall is 

 sufficiently high. 



