220 Nitrification in Eijyptian Soils 



of the nitrate content of the soil. In the following study, the amount 

 of nitrate present in the soil has been taken as an index of bacteriological 

 activity. This method has found successful application in other parts 

 of the world and without doubt is one of the simplest and best. More 

 recently, the determinations of soil nitrates have been supplemented 

 by bacterial counts and by observations on the atmosphere surrounding 

 the soil particles^. 



Under the conditions of the writer's laboratory, it has been difficult 

 to supplement the nitrate values except in some special cases. 



The amount of nitrate found in the soil at any moment is usually 

 the result of the balance between crop requirements, drainage and 

 nitrification. In Egypt there is fittle or no drainage under normal 

 conditions, on the other hand other movements of soil water are of 

 importance, such as the vertical movements due to capillarity and 

 lateral movements due to seepage. In the first case salts accumulate 

 on the higher portions of the soil such as the tops of ridges, while in 

 the latter case considerable areas at lower levels are affected. In some 

 cases nitrates in considerable quantities may be found out of the reach 

 of plant roots on the tops of ridges which only receive water from below 

 by capillarity. A case of this kind is quoted in connection with a maize 

 fiekP. 



The case of fallow land with its accumixlation of nitrates so well 

 known in England is of special interest in Egypt. Fallow soils in Egypt 

 may be and frequently are biologically dormant ; in some cases, as in 

 the basin lands of Upper Eg^'pt, for several months each year. The 

 water supply has been cut off and moisture conditions are therefore 

 unsuitable. The fallow periods of the Egyptian farm rotation are 

 particularly interesting on this account. 



When a crop is grown on the land nitrate is removed from the soil 

 fairly rapidly. In the case of wheat and maize there is usually no 

 accumulation of nitrate in the soil, but the case of cotton is remarkable 

 in that apparently, in the early stages of growth at least, nitrification 

 is well ahead of the needs of the plant and appreciable quantities of 

 nitrate accumulate in the surface soil. 



' See for example: E. J. Russell, This Journal, 1914, 6, 18; E. J. Russell and A. Apple- 

 yard, This Journal, 1915, 7, 1 ; E. J. RusseD and A. Appleyard, This Journal'Vill. 8, 385. 



2 See also V. M. Mosseri, "Note preliminairc sur les sels nuisibles et le cotonnier en 

 Egypte," Trans. Zrd Intcrnalional Congress of Tropical Agricultnre. London. 1914. 



