J. A. Prescott 219 



The important work of W. L. Balls on the physiology of the Egyptian 

 cotton plant has thrown considerable light on the factors limiting the 

 growth of this crop, and undoubtedly other factors, such as water supply 

 and temperature, limit the growth and ultimate yield of the cotton crop 

 far more than does the food supply. 



As an outcome of the results obtained by the study of the soil of 

 cotton fields during the past two years and described in the following 

 pages, the writer has a suggestion to make concerning this problem of 

 the nutrition of the Egyptian cotton plant, at least as far as the nitrogen 

 is concerned. 



The cereals of Egypt, however, are in a very different position. 

 To persons accustomed to hear of the inexhaustible fertility of the 

 Nile valley it comes somewhat as a shock to learn how dependent the 

 maize and wheat crops are on nitrogenous fertilisers. The rapid increase 

 in the sales of nitrate of soda during the past ten years and the exploita- 

 tion of all local sources of nitrogen, such as the debris of ancient villages 

 (Koufri), are .signs that the fertility of Egyptian soils is indeed not per- 

 manent under the modern system of perennial irrigation. The lack of 

 fuel is so pronounced in Egypt that all crop residues are gleaned from 

 the land for this purpose and all solid excrements of farm animals are 

 converted into fuel. At the time of writing, cotton seed cake, containing 

 4 % of nitrogen, is one of the most important commercial fuels of the 

 country. The use of green manures, in the real sense of the term, is 

 quite unknown in Egypt. 



The value of the leguminous crop, Bersim, in maintaining the 

 fertility of the soil is well known by the farmers themselves and when 

 fed on the land a considerable proportion of nitrogen is added to the 

 soil. Under these conditions the amount of nitrogen added to the soil 

 by the bersim crop ought to be sufficient to carry forward the rotation 

 of three years, with a little artificial aid to the maize crops. 



The residues of the bersim alone without any return to the land in 

 the way of animal excrements would seem however to be insufficient 

 for the successful growing of cereal crops. 



Nitrification in Egyptian soils. 



Up to .the present time no definite series of observations has been 

 made in Egypt concerning the activity of soil bacteria in producing 

 plant food. Beyond the general statement by Roche, already mentioned, 

 that nitrification does take place, no evidence for example is available 

 concerning the intensity of the process as determined by the fluctuation 



