Agriculture Reference
In-Depth Information
Figure
9.17.
Mountainous watershed, covered with trees, on the island of Leyte. In the fore-
ground is the Camote Sea.
Rainwater can be conserved for agriculture in several ways. Cultivation can be
carried out in such a way—with contouring, strip cropping, and conservation
tillage—to maximize infiltration into the soil. This will both provide water for crops
and allow more water to move through the soil profile and into the groundwater. It is
also possible to store rainwater by the use of cisterns (sealed), ponds, or other catch-
ments. However, such storage of rainwater is not as good overall as storage in soil.
For example, Ferrie, a farmer in Zimbabwe, has a large granite rock outcrop
§
behind
his house. He collects rainwater, which runs off this rock and channels it into cisterns
around his house. The cisterns are not sealed and the water percolates horizontally
down slope from these cisterns, providing subsurface water for a myriad of crops
that are planted in plots situated down slope from the cisterns.
Another water storage system is called a watershed (Fig. 9.17). This is often a
mountainous or sloping area that is heavily wooded. Trees and associated soil hold
water that is slowly released into the surrounding environment, usually in the form
of springs, streams, and rivers. When managed correctly, watersheds can be a source
of continuing clean water for animal and human consumption. If the watershed is
large enough, the water it releases may also be used for irrigation.
Great care must be exercised when using water from other sources, that is, other
than watersheds and rainwater, for drinking, irrigation, or other agriculture purposes.
There are two reasons for exercising caution: excessive use of well water may cause
the well to go dry, that is, the water is being used faster than it is replaced. The
second reason is that water from wells, streams, rivers, lakes, and ponds may contain
salts or toxic compounds or elements. There are many places in the world where this
happens; for example, Bangladesh has toxic arsenic levels in some well water, and
§
Rock outcrops describe any situation where rocks stick out of the soil.
