32 EGYPTIAN AGRICULTURE. 



The soil, however, seldoms suffers from too much plant 

 food ; but it is often too salt through the presence of too 

 much sodium chloride, sodium carbonate, calcium chlo- 

 ride, magnesium sulphate, etc. Some salts are more 

 harmful than others, thus sodium carbonate, an alkaline 

 salt, is more hurtful to plant growth than sodium chloride. 

 The reason of this may be due to the neutralising action 

 of an alkaline salt on the plant root juices : the alkaline 

 salt paralyzes the efforts of the plant to prepare its food. 

 Again calcium chloride is a hygroscopic salt and has 

 a tendency to keep the soil in a constantly wet, sticky 

 condition. 



Salt soils owe their saltness chiefly to the conditions 

 under which they were formed or exist. Some soils are 

 salt because they were formed at low levels near the sea 

 water; and many are salt because, through infiltration or 

 other cause of high water table, much of what is really 

 drainage water is being raised to the surface by capillarity, 

 evaporated, and the salts left to accumulate in the soil. 

 The very deep lying salt does not usually come to the 

 surface except on low lying lands, but by diffusion, salts 

 can move up in the soil without any upward movement of 

 the body of the water. In Egypt wherever a soil has no 

 drainage salt always appears. Besides the direct effect which 

 the presence of an excess of soluble salts has on the root 

 of the plant and its power of absorption, salts are harmful 

 through retarding organised activity and the preparation 

 of plant food in the soil. Again, the constant soaking of 

 the soil particles in a salt solution, results in the washing 

 out of much of the plant food from the soil when the soil 



