SOIL FERTILITY 



special diet. The two classes of fertilizers are 

 often combined by using the natural fertilizer as 

 the general food for the whole garden, and by 

 adding in the row a small amount of special fer- 

 tilizer; for example, a pint of ground bone or 

 bone meal to a ten-foot row of peas, is mixed 

 thoroughly in the bottom of a four-inch trench and 

 covered with a light layer of soil, before the peas 

 are planted, so as to give them a good start. 



Of some seventeen elements required for plant 

 structure, about half a dozen are all-important. 

 For the needed small quantities of the others, 

 the plant may be left to shift for itself. Of the 

 important ones, oxygen comes from the air, from 

 water and from chemical disintegration. From 

 the chemical separation of water comes hydrogen. 

 Nitrogen has been accounted for. From 50 to 

 90 per cent of the food of plants is taken from the 

 air, and three-fourths of that percentage is carbon 

 derived from carbonic acid gas. Potash and 

 phosphates come from decaying animal and 

 vegetable matter and from the fertilizers used. 

 Lime, iron, sulphur and magnesium are indispens- 

 able.* They usually, however, exist in sufficient 

 quantities in the soil, and are found in some 

 measure in the fertilizers discussed. 



or leguminous plants. Never use nitrate upon these nitrate making 

 factories. 



Commercial fertilizers are better used on clay soils for they are 

 not as liable to be washed out and the chemical action they set up 

 disintegrates the clay particles. 



♦Osterhout, W. J. V.: Experiments With Plants, p. 139. 

 107 



