Full Product Manual

Determine Plant Water Requirements Page 21
Calculating Water Requirements
Begin by filling in the identifying information about the site and the hydrozone
at the top of the worksheet. Transfer the Daily PET, Application Efficiency, and
Soil Type from the Dense Hydrozone Worksheet (Figure 7-1 at the end of Chapter
7) to the appropriate places on the dense and sparse hydrozone worksheets
(Figures 4-1 and 4-2, page 20). This information will be very important when you
compute the water requirements of the individual plants in the hydrozone.
Be sure to write the number of the hydrozone in the box at the upper right corner
of the worksheet. You may also want to include a one- or two-word description,
such as “front planter.”
∂ Gather Site
Information
∑ Calculate K
c
As described in Chapter 3, the potential evapotranspiration rate (PET) describes
the amount of water used by a specific variety of grass under ideal moisture
conditions. To calculate the exact water requirement of an individual plant, you
must adjust PET to account for specific conditions and the needs of the plant. The
adjustment factor is called the plant’s “K
c
”. The terms “crop coefficient” and
“plant factor” are also sometimes used.
Use the spaces on the worksheets to calculate K
c
for each plant in your
hydrozone. Note that for densely planted hydrozones there are separate spaces
for recording information on base plants and non-base plants.
TABLE 4-1: BASE PLANTS IN DENSE HYDROZONES
Planting Scheme Base Plant
Ground cover only Ground cover
Ground cover and trees Ground cover
Ground cover and shrubs Ground cover
Shrubs and trees Shrubs
Shrubs only Shrubs
Ground cover, trees, and shrubs Ground cover
Dense Hydrozones Only
In a densely planted hydrozone, you must first identify the “base plant.” The
base plant is the plant material in the hydrozone that uses the least amount of
water per day. Often, it is also the plant that covers the majority of the planted
area—generally either ground cover or shrubs. Use Table 4-1 to help you identify
the base plant for your hydrozone.
Plant Species
It’s very important that you accurately list each of the plants in the hydrozone. In
some cases, this information will come from the planting plan; in other cases, you
will collect the data from an actual site survey.
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