94 



FIRST YEAR SCIENCE 



holding water, it furnishes plant food and it keeps the 

 soil from getting too compact. 



In sandy soils there is usually little humus, the water 

 soon drains out of them and plants become parched. Such 

 soils warm up quickly in the spring and dry out rapidly 

 after long wet spells. When humus and plant food in 



the form of manure are 

 added they are especially 

 adapted for growing 

 early crops and crops 

 that do not require a 

 great deal of moisture, 

 such as grapes. The 

 " Fresno Sand " of Cali- 

 fornia and the sandy 

 coast plains of the east- 

 ern United States are 

 soils of this kind. 



In clay soil the parti- 

 cles are extremely small, 

 as are also the spaces 

 between the particles. 

 Water is therefore taken 

 up very slowly. It is, 

 however, held tena- 

 ciously. When clays 



become wet, they are very sticky and cannot be worked. 

 When they dry, they become very hard and crack. 

 If cultivated at the wrong time they break into hard 

 lumps and render further cultivation difficult. The 

 adobe soil of the west is of this character. If the soil is 

 nearly pure clay, it is useless for farming. If sufficient 

 sand or humus can be added, it becomes valuable, since 

 clays usually contain the elements needed by plants. 



ADOBE SOIL. 



A heavy clay soil, very fertile, but hard 

 to cultivate. 



