THE FERTILITY OF THE SOIL 21 



sion of the films of water around the soil particles heconiing 

 greater as evaporation from the upper surface of the soil takes 

 place. One of the most important problems in farming is to 

 conserve this soil moisture and prevent its evaporation. 



Amounts of Capillary Water Held by Soils. — Sandy soils hold 

 very little capillary water. After a rain it is estimated that 5 

 to 10 per cent, by weight of the soil will be water. Sandy 

 loams and silt loams retain 15 to 20 per cent, and heavy clay 

 soils 30 to 50 per cent. Heavy clay soils are suitable for grass 

 lands because of this power of holding water, as grasses re- 

 quire considerable water for maximum growth. 



How to Prevent Loss of Capillary Water. — As capillary water is 

 so important for the welfare of crops we should learn how to 

 prevent its loss. Water will follow along the path of least 

 resistance. So if we form a soil mulch by cultivating or stirring 

 the soil to the depth of two or three inches we will ofifer re- 

 sistance to the upward movement of water. The soil should not 

 be cultivated too deeply because some of the small roots are lia- 

 ble to be injured. 



How to Increase the Upward Movement of Capillary Moisture. — 

 When seeds are planted in dry seasons it is often advisable to bring 

 up the water to aid in their germination. This may be ac- 

 complished by rolling the soil thus making it firmer. After 

 rolling it is important to form a soil mulch again to prevent the 

 loss of all the water.* 



3. The Biological Condition of the Soil. — All cultivated produc- 

 tive soils are full of organisms, both animal and vegetable, which 

 aid in furnishing plant food. There are many different organ- 

 isms whose functions vary a great deal. Most of these organ- 

 isms are so small that they cannot be seen without the aid of 

 the microscope, while some, with which we are all familiar, 

 are large. 



The rodents, worms and insects all have their place in stirring 

 the soil although the rodents and some of the insects are in- 

 jurious to crops. Plant roots are beneficial in that they leave 

 organic matter in the soil and openings for the access of water 

 and air. 



