44 EGYPTIAN AGRICULTURE. 



constant movement and renewed ; in stagnant water or below 

 the water table no crop roots can live because standing water 

 contains little or no air. In wet soils soils in which the water 

 table is near the surface the spaces normally filled with 

 air contain water, and in such soils the plant roots quickly 

 decay. This unhealthy state of the plant root may often 

 be observed in the case of cotton growing on land which 

 is wet at high Nile. The available air in the soil is that 

 which is dissolved in the soil water. For germinating 

 seeds a very free supply of air is necessary, and it is chiefly 

 the lack of air which causes the failure in the growth of 

 seeds which are watered directly after sowing. The 

 nitrogen gas of the soil being dissolved in the soil water 

 enters the roots of the leguminous plants and supplies the 

 nitrogen fixing organisms with matter to elaborate into 

 plant food. Hence the nodules of the leguminous plants 

 are usually best developed in dry sandy soil. Good culti- 

 vation and drainage help to insure a good ventilation of 

 the soil. 



WATER IN ITS RELATION TO THE SOIL. 



A regular supply of water in the soil is absolutely neces- 

 sary for plant life. This supply must be neither too great 

 nor too little and the water must be constantly moving. 

 Water enters largely into the composition of most crops ; 

 it is necessary to dissolve and carry plant foods into the 

 plant root ; it tends to maintain an even soil temperature; 

 it softens and makes easier the penetration of roots in the 

 soil ; in draining away it removes waste materials and 

 salts; it renders the growth and activity of micro-organisms 



