J. A. Fkescott 233 



It might be expected that as soon as conditions again became 

 favourable for biological activity, an abnormal increase in such processes 

 as nitrification would take place. E. J. Russell and H. B. Hutchinson ^ 

 suggest that prolonged drought or prolonged heating at 40° C. acts on 

 the soil in the same way as partial sterilisation by heat or by volatile 

 antiseptics. No doubt in the case of the basin lands some such action 

 does occur and to a less extent in the ordinary sheraqi soils of Lower 

 Egypt. The conditions are not quite stringent enough in the case of 

 the latter soils to kill off all the protozoa which are readily found in 

 sterile hay infusion which has been inoculated with sheraqi soil. In the 

 case of the basin samples however, very few protozoa developed, chiefly 

 ciliates, and these were by no means vigorous. The proof of the partial 

 sterilising efltect of the sheraqi conditions is rather difficult to obtain, 

 as it is obviously difficult to keep the same soil untreated for comparison. 

 The writer has made preliminary attempts to settle this interesting 

 point, but further study will be necessary before final evidence can be 

 obtained. 



The sHiiniier falloiv subsequent to the sheraqi period. 



Frequently after a bersim crop, the summer fallow is extended 

 beyond the sheraqi period until the winter, when a crop of wheat is 

 grown. The irrigation necessary is given after the requirements of the 

 maize crops have been satisfied. During the summer of 1917, the amount 

 of nitrate accumulated in such soils was determined in a few instances. 

 A piece of land after wheat, reserved for such a fallow, showed an increase 

 in nitrate content from 14 to 23 parts per million in one month. Another 

 piece of land after bersim contained 26 parts per million on the 

 3rd November after being fallow all the summer; in this case no special 

 effort had been made to keep the soil moist after the first irrigation 

 and ploughing. The possibilities of the active summer fallow were 

 illustrated, however, in the case of two fallow pots containing forty 

 kilos each of soil, which were kept at 20 % moisture content for three 

 months diiring the summer of 1917. The amount of nitrate in the soil 

 increased from 10 parts to 2.50 parts per million during this period. 

 Under practical conditions it would hardly be possible to obtain such 

 active nitrification in the summer fallow — and possibly not advisable 

 to attempt it. All that is necessary is to obtain a sufficient accumulation 

 of nitrate in the soil to give the wheat crop a good start, relying on the 



1 This Journal, 1913, 5, 152. 



