te and appear so quickly. The soil has also been
firmed about them. Hence they have a firmer hold on the soil and but
few of them are destroyed if the work is carefully done.

In working crops not only should weeds be destroyed but also surplus
plants of the crop, as these have the same effect as weeds; namely,
they occupy the soil and take plant food and moisture which if left to
fewer plants would produce a larger harvest.

HILLING AND RIDGING

Except in low, wet ground, the practice of hilling or ridging up crops
is now considered by those who have given the matter thorough study,
to be unnecessary, flat and shallow culture being cheaper. It saves
more moisture, and for this reason, in the majority of cases, produces
larger crops.

Sometimes during very long-continued periods of wet weather weeds and
grass become firmly established among the plants of the crop. Under
such circumstances it is necessary to use on the cultivator teeth
having long, narrow sweeps that will cut the weeds just beneath the
surface of the soil. Sometimes a broad-toothed tool is used that will
throw sufficient soil over the large weeds near the rows to smother
them.

The condition to be met and the effect of the operation should always
be given serious thought.

We have considered after-cultivation as influencing soil fertility by
checking a loss of water by evaporation and weed transpiration, and
this is its main influence but other benefits follow.

Keeping the surface soil loose and open benefits fertility because it
directly aids the absorption of rain, favors ventilation, and has a
beneficial influence over soil temperature. Indirectly through these
factors it aids the work of the beneficial soil bacteria and the
chemical changes in the process of preparing plant food for crop use.

CHAPTER XIX

FARM MANURES

FUNCTIONS OF MANURES AND FERTILIZERS

In Chapter II we learned that the roots of plants for their growth and
development need a soil that is firm yet mellow, moist, warm,
ventilated and supplied with plant food. We also learned that of the
plant foods there is often not enough available nitrogen, phosphoric
acid, potash and lime for the needs of the growing plants.

Manures and fertilizers are applied to the soil for their beneficial
effects on these necessary conditions for root growth and therefore to
assist in maintaining soil fertility.

CLASSIFICATION OF MANURES AND FERTILIZERS

Manures may be clas