THE SOIL AND ITS IMPROVEMENT 



91 



Very few other plant-foods need give a gardener much con- 

 cern^ as they are usually present in garden soils. 



Commercial fertilizers are ' purchased in great abundance 

 in the eastern and southern states and for special crops in other 

 sections. Millions of tons are purchased for use each year. 

 The application of commercial fertilizers as a rule is of no 



Fig. 57. — Manure for gardens should be well rotted, as it will then contain less weed 

 seeds; but it should not be allowed to leach in the weather. (U. S. D. A.) 



permanent benefit to the soil itself. The more permanent 

 amendments for soils are barnyard manure and green manure. 



Commercial fertilizers vary in their composition aiid are 

 valuable in proportion to the amount and kind of the three 

 main foods contained in them. 



Nitrogen is the most expensive fertilizer, and soils are 

 more commonly in need of it. Yet this element may be 

 obtained freely from the air by the continuous growth of 

 legumes.. As fertilizers containing nitrogen become available 



