SOILS I5I 
This consists of plowing, harrowing, disking, or using some 
other form of cultivator. The plow is the implement upon 
which we chiefly rely for turning the ground to a sufficient 
depth for the deeper roots of the plants. Plowing loosens 
up the soil to the entire depth of the furrow, making it easier 
for the roots to penetrate, for the rain to soak in, and for 
the air to enter. It turns under manures, stubble, and other 
plant matter most thoroughly and buries them com- 
pletely. The other tools are used merely for shallow tillage 
having for its purpose preparing a good seed bed, main- 
taining a dust mulch or blanket, or destroying weeds. By 
a dust mulch we mean a shallow surface layer of earth so 
loose and porous that moisture cannot rise through it from 
below and escape by evaporation. It is the farmer’s most 
efficient means for the conservation of soil water. 
Fertilizers. — We have learned that a productive soil must 
be mellow and warm and be well supplied with humus, water, 
air, and plant food. As a means of securing and maintaining 
these conditions, manure and other fertilizers are applied. 
On the ordinary farm we rely chiefly upon stable and barn- 
yard manure. That contains all the necessary elements of 
plant food, and as it decays it produces gases that aid in 
dissolving the mineral matter in the soil and thus make it 
available for plants. But more important still, it adds 
organic matter to the soil and thus improves its texture, 
making it more mellow, porous, and warm, giving it more 
power to hold moisture, plant food, and air, and making it 
more hospitable to soil bacteria. 
Almost all plant material serves the purpose of restoring 
humus to the soil. The roots and stubble of crops are of 
some value, but newly broken sod contains a great deal more 
vegetable matter and, therefore, it is very beneficial to grow 
