HELPING PLANTS GROW 7 



in soil water. Our problem is to make conditions as favor- 

 able as possible for plants to meet these needs. A study of 

 them will show that we have little or no control over sun- 

 shine and the air above ground. The chief way for us to 

 help the plant therefore is through the soil. By means of 

 various farm operations on the soil it is possible to control, 

 to a considerable extent, the water supply and the air needed 

 by the roots, and to furnish material containing such chemical 

 elements as nitrogen, phosphorus, and potassium, in ac- 

 cordance with the needs of the plant. 



This fact suggests the soil as the most appropriate subject 

 to consider next in our study of agriculture. It is so important 

 that we must study it in detail. Especially should we know 

 what it is and how it is related to water supply, to air, and 

 to plant food. 



