30 EGYPTIAN AGRICULTURE. 



ium, iron, and sulphur, usually occur in the soil in such 

 comparatively large quantities that they are never specially- 

 applied in manuring. The manures generally applied to 

 the soil to increase the crop are the nitrogenous, phosphatic 

 and potassic. The soil may be regarded as a reservoir of 

 plant food which, through the action of the weathering 

 agents, is digested and dissolved to suit the requirements 

 of the plant. 



Analysis of a fair soil : 



Nitrogen Oil % 2.000 kilos, per feddan. 



Potash 0'70 % = 13.230 ,, 



Phosphoric acid ... 0'40 % = 7.560 

 (Calculated in a layer of soil 30 cm. deep). 



This is as much nitrogen as is contained in 73 crops 

 of cotton, and as much phosphoric acid as in 750 crops. 

 It is evident, that even a very poor soil contains far more 

 plant food than is required by an ordinary crop, but it 

 is known by experience that even the best soils give an 

 increased crop when manure (available plant food) is 

 applied to the land. Of course one of the objects of apply- 

 ing manure is to maintain the fertility of the soil. These 

 figures show clearly that the fertility of a soil depends 

 on the amount of food available for the crop and not on 

 the total food as shown by analysis. The nitrogen, in the 

 soil, as nitrates, seldom exceeds 1 kilog. per feddan at 

 any time. 



The following table gives the analysis of three soils 

 with their sub-soils, and the crops of cotton produced from 

 each. 



