62 Gardening 
Fic. 40. Spreading manure over the garden. The coarse lumps should be 
broken up and the material spread evenly. Many gardeners prefer putting the 
manure into the trench direct and spading it under, instead of scattering it over 
the surface of the soil. : 
SOIL FERTILITY 
The soil is more than a place for the roots of plants to 
grow. It supplies water and raw food materials on 
which the plant lives. I¢ is itself raw food material 
for plants, as plants actually take into themselves certain 
compounds contained in the soil and change these mate- 
rials into substances which build the plants up. A rich 
soil is one that supplies in large amounts the materials 
that the plant needs. Of these, aside from water, the 
ones that are most often lacking in sufficient amounts 
are nitrogen, potassium, phosphorus, and lime. 
The food materials are constantly being removed 
from a cultivated soil in the crops harvested, and are 
also being lost in the drainage water. Therefore it is 
often necessary to furnish new supplies of these materials 
to keep a soil from becoming poorer and less productive. 
They may be added to the soil as manures, compost, 
