Code of Practice - Irrigated Public Open Space - SA Water

Using the above climate data the evapotranspiration from a
reference crop (tall cool season grass (lucerne) grown to a
height of 12cm which covers the ground and is supplied
with adequate water), can be calculated. The result is
reference evapotranspiration (ETo). ETo is calculated by the
Bureau of Meteorology (BoM) and is published on their
website or can be accessed from private weather stations in
regional areas where the BoM does not have stations.
As the water requirement varies for different turf species
under different growth conditions the ETo must be
converted to evapotranspiration for a specific crop (ETc).
A crop co-efficient (Kc) is required to covert ETo to ETc.
Crop co-efficients (Kc) for turf grassareasfollows.
Table No 2 - Turf Grass Crop Co-efficients (Kc)
TurfType Warm Season Cool Season
Turf Grass Turf Grass
Couch sp. / Kikuyu Rye sp./Bluegrass/
Fescue
Crop Co-efficient( Kc ) 0.6 - 0.8 0.8 - 0.95
Note: Kc = 0.7 has been used in calculations in the Code.
Crop Stress Factor (Ks) is applied where a management
decision has been made to reduce the vigour and quality of
the turf grass.Asdetailedpreviously,irrigatedpublicopen
space can be classified into four TQVS standards depending
on the function and required standard of the turf surface.
The Ks effectively reduces the irrigation requirement to
achieve the appropriate functional outcome of the turf.
Crop stress factors for IPOS are as follows;
Table No 3 – Turf Grass Crop Stress Factors (Ks)
TQVS Cat. TQVS 1 TQVS2 TQVS3 TQVS4
Description Passive
Elite Premier Local Recreational
Sports Turf Sports Turf Sports Turf Turf
Crop stress
factor (Ks) 1.0 0.6 0.5 0.4
The calculation for ETc is;
ETc = ETo x Kc x Ks
ETc = ETo x 0.7 x 0.5 (TQVS 3)
5.0 TURF & IRRIGATION MANAGEMENT PRINCIPLES
18
Effective Rainfall (Pe)
Rainfall or precipitation (P) replaces water lost from the soil
by evapotranspiration and thereby reduces the Net
Irrigation Requirement (In). Rainfall (P), during the
irrigation season can be variable and is not always effective.
Small rain events are lost by evaporation and do not soak
into the soil, whereas large events may deliver more water
than the soil can hold and can be lost either through
drainage or run off.
A general rule for a shallow rooted turf grass crop is that
only half the rainfall that occurs in the irrigation season is
effective and actually replenishes soil to the root zone of the
plant. The Effective Rainfall Factor (Pf) used in the Code is
0.5 or 50%. When this is multiplied by the total rainfall,
Effective Rainfall (Pe) is calculated.
Rainfall data can be accessed from the BoM website or
from local rain gauges.
The calculation for effective rainfall is;
Pe = P x Pf
Where:
Pe - Effective rainfall (mm)
P - Total rainfall (mm)
Pf - Effective rainfall Factor (decimal factor)
Application Efficiency (Ea)
Irrigation systems do not apply water at 100% efficiency.
The optimum performing irrigation system is subject to
inherent system inefficiencies. Factors such as wind,
misting, poor sprinkler spacing, nozzle loss and other
system performance faults impact on the uniformity of
water application. Therefore a factor must be applied to
account for irrigation system performance.