Perhaps its most
valuable single asset from the human viewpoint is its topsoil. Topsoil
plus light, air and moisture provide the elements necessary for
producing vegetation. Vegetation, in its turn, furnishes the nourishment
on which animals thrive.
At the top of our priority list for the well-being of the earth stands
the injunction: conserve and build topsoil.
Topsoil is lost through erosion--wind erosion, water erosion, erosion
through over cropping. It is held in place by stones, grasses, and the
roots of shrubs and trees. Untouched by human hands, on the prairies and
in the forests, topsoil is deepened year by year as winter frosts break
up soft rocks, as dead grasses, leaves, twigs break down into humus, to
become part of the topsoil and provide the nourishment for a new round
of vegetation.
Topsoil is renewable, replaceable. Lost through cropping and erosion, it
may be rebuilt and deepened by natural processes. In temperate climates
with normal rain and snowfall, the topsoil of grasslands or a forest may
be deepened year by year and century by century. Topsoil may also be
deepened by dust storms that pick up particles of humus from dry lands
and carry them to moister areas.
Through a carefully controlled sequence, semi-desert lands planted first
to grasses and then to shrubs and trees can be protected against wind
erosion. As vegetation flourishes it increases dew formation and
rainfall.
Pages:
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313