34 EGYPTIAN AGRICULTURE 



desirable. Roughly Q'2% of soluble salt is too much and 

 rO/^ renders the land infertile. With pot experiments 

 2-0 % sodium .chloride; 2'0 % sodium nitrate; 1'0 % 

 calcium chloride ; O'l % mercuric chloride on wheat 

 prevented the production of any grain. 



The presence of: much acid in the soil is injurious to 

 plant growth. Soil acidity is only found in soils very rich 

 in organic matter, and is due to the decomposition of this 

 organic matter and the formation of complex organic 

 acids. The conditions predisposing to acidity are deficient 

 drainage and aeration, and the absence of anything in the 

 soil capable of neutralising the acids formed. In Egypt, 

 acid soil is practically unknown, as usually the soil is not 

 particularly rich in organic matter and always contains 

 a sufficiency of lime compounds. Good agricultural land 

 should show a neutral or slightly alkaline reaction as these 

 states most encourage the bacterial growth which plays 

 so great a part in the preparation of plant food. Strong 

 alkalinity is as undesirable as acidity. 



Of the chemical actions taking place in the soil, the 

 fixation of plant food is one of the most important. When 

 solutions containing compounds of potassium, phosphoric 

 acid, and ammonia, are filtered through a good loam soil it 

 is found that the drainage water contains very little of 

 those bodies in solution. This is partly due to the foods 

 having formed, with certain of the soil constituents, insoluble 

 compounds which are unable to drain through the soil. 

 On the other hand, nitrates form no insoluble compounds 

 with any constituent of the soil, and therefore they pass 

 through. Hence, although drainage water contains nitrates 



