Horticulture Principles and Practices

FIGURE 4–19 Furrow irrigation
of lettuce. (Source: USDA)
irrigation is commonly used in orchards (Figure 4–18). Furrow irrigation is a version
of flood irrigation in which the surface flow is limited to channels between ridges.
Vegetables may be irrigated in this way (Figure 4–19).
4.8.9 SOURCE OF WATER
For home gardening, municipal water is the most frequent source of water for irrigation.
The advantage of this source is that it is ready for use, provided the user has a means of
connecting to it, eliminating the initial cost of providing an irrigation system. The source
is reliable, since water is needed each day for a variety of uses in the home; the city ensures
a continued supply. The disadvantages of this source of water are its high cost, the
possibility of rationing in certain areas at times when plants need water the most, and the
sensitivity of certain plants to municipal water treatments (chlorine and fluoride).
For a large landscape, a well may be an alternative source of water. Wells are practical
where the water table is at a readily accessible level. Sinking a well is expensive,
and the quality of water is affected by soil and rock materials and may yield hard water
(containing rock mineral deposits). Underground water may be contaminated by soil surface
pollutants. Three types of wells may be used for irrigation. Driven wells are relatively
inexpensive and easy to install. The unit is small and thus unobtrusive in the
landscape. However, it yields a limited amount of water and is prone to blockage from
debris over time. Driven wells are practical in areas where the water table is high. A well
point must be found, which is perhaps the most difficult aspect of the whole process.
Once found, shafts are driven into the soil using a sledgehammer. Shafts may each be
about 5 feet long (1.5 meters) and are driven one after another, connecting the sections
as one proceeds. Dug wells take up more space but also yield more water. If the site is
properly selected, a dug well produces good-quality water year-round. A pump is needed
to lift the water for use; dug wells may be lined with rock or concrete. The third type of
well, a drilled well, is rather expensive and not a common option for homeowners. It is
installed by using large drilling equipment similar to that used for prospecting oil.
Driven Well
A method of drawing
groundwater by driving
shafts into the water table.
4.8.10 WATER QUALITY
Water quality for irrigation is not only critical to the success of growing plants but it also
affects the design of irrigation systems. The issue is less critical if municipal water is the
water source for irrigation. Water quality problems may be physical, biological, and
chemical. The physical problems relate to the presence of mineral particles—sand, silt,
and clay—in the water source. These sediments can clog pipes and sprinkler nozzles.
Chemical problems pertain to the presence of dissolved salts like calcium, magnesium,
4.8 Soil Water 135