LUTHER BURBANK 



absent from any kind of soil. It does happen 

 sometimes, however, that an element is not present 

 in available form. The plant's roots, of course, 

 cannot take up certain elements that are in such a 

 form that they cannot be absorbed. When the 

 supply of material in the form that can be used is 

 exhausted, the plant does not thrive. 



Quite often the failure of crops when it can be 

 definitely attributed to the condition of the soil is 

 due to an unfavorable physical condition rather 

 than an unfavorable chemical condition. 



Rotation of crops always has an important and 

 essential effect upon the physical condition. When 

 alfalfa, cow peas, clover, or some other legume is 

 grown, the roots grow deeply into the soil and 

 when another crop follows, the fissures or canals 

 opened up by these deep growing roots are used 

 by the roots of the new crop, besides storing con- 

 siderable nitrogen. In this way it is much easier 

 for the following crop to permeate the soil where 

 there is plenty of moisture. The roots can develop 

 much more quickly and with less effort than if the 

 deep rooting crop had not been grown on the soil 

 before it. 



It is quite evident that the addition of barnyard 

 manure has almost as much beneficial effect upon 

 the physical and bacterial condition of the soil as 

 upon its chemical condition. 



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