296 GENERAL SCIENCE 



tions of different fertilizers may be used. The yields in the 

 different boxes will give a definite measure of the relative 

 value of the different fertilizing materials on the soil tested. 



FIG. 255. Showing the Value of Lime on Sour Soil. 



The experiment station bulletins of the different states 

 usually give quite accurate information concerning soil 

 fertility and the materials needed in fertilizers. " On 

 practically all Ohio soils that have been for any length 

 of time in cultivation, possibly excepting mucks, phos- 

 phorus must be supplied before the maximum yield of any 

 crop can be attained. The longer the land has been in 

 cultivation, the greater the need of phosphorus." l 



Why we Cultivate. There are a number of reasons for 

 cultivating the soil while crops are being grown. Culti- 

 vation destroys weeds which would otherwise take the 

 1 Ohio Circular No. 79. 



