To sink surface stones so that they will not interfere with harvesting
the crop.

Light porous soils may be rolled at any time, but clay soils can be
rolled to advantage only when they are stiff and cloddy.

Spring-sown grain is often rolled as soon as sown. This is all right
in ordinary spring weather, but if showers are frequent and the soil
is quite moist the rolling should be omitted till after the grain is
up. The same practice will apply to autumn-sown grain also. If the
soil is dry the rolling helps it to pump water up to the seeds. But if
it is moist and showers are frequent the combined action of the
roller and the rain is to make so thick a crust that many of the seeds
will not be able to force their way through it or will be smothered by
poor ventilation. After the grain is up the rolling may be done to
advantage, as it then makes a firm soil about the roots of the plants,
a condition of benefit to grain crops.

The most simple form of roller is a solid or hollow cylinder of wood
fastened into a frame by which it is drawn. Some rollers have spikes
or blunt attachments fastened to their surfaces for breaking clods. A
roller that is quite popular consists of a cylinder of pressed steel.




CHAPTER XIII

LEAVES