60 FIELD AND LABORATORY STUDIES OF CROPS 



the roots are similar to tap roots which have a tendency to 

 go down in search of moisture and food, and that gradually 

 lateral roots are formed. In the course of sixty or seventy 

 days the soil will be filled with roots from hill to hill. If 

 shallow cultivation has been practiced, these roots will 

 come near the surface of the soil, where they will find the 

 greatest amount of available plant food. 



After a heavy ram the greater part of the water which 

 enters the soil passes down through until it reaches a place 

 where all of the openings between the soil particles are com- 

 pletely filled with free water. During the time between 

 rains, the plants must get their moisture from this supply 

 deep down in the soil. The process by which this water 

 rises in the soil is called capillarity. This capillary water 

 is sometimes called film moisture, because it is spread out in 

 a thin film over each soil particle. Persistent shallow cul- 

 tivation forms a mulch over the surface of the soil and pre- 

 vents excessive loss of moisture by evaporation. 



