Page 110 - GRIHA Manual Volume II - Introduction to National Rating System
P. 110
102 Griha Manual: Volume 2
Irrigate at the right time
Irrigate as infrequently as possible. Only when plants have used most of the available soil moisture
the next irrigation should begin. In general, irrigating once or twice a week is ideal. Irrigation timing
can be determined in two ways. The first method is to monitor the plants and/or soil in the landscape
or garden. The second method is to determine the amount of water that has been lost from the
landscape and how much will be needed to replace it.
Scheduling irrigation based on observation
Optimum irrigation requires irrigation just prior to water stress. However, if a little stress can be
tolerated, timing can be determined by careful observation of the landscape to notice the symptoms
of early water stress. Green lawn grass will begin to change from a bright green colour to a dull
colour when they become water stressed. They also lose their ability to spring back rapidly from foot
traffic, so a dry lawn will show visible footprints for a longer period of time. Another observation
method is to use indicator plants to predict irrigation needs. Almost every landscape has a shrub
or plant that wilts sooner than any other plant in the landscape. This plant can be used to indicate
the time to irrigate. Occasionally plants may wilt under hot, dry conditions even if the soil is moist.
Therefore, soil moisture should also be determined.
Scheduling irrigation based on evapotranspiration
Irrigation scheduling can also be determined by using evapotranspiration (ET) data. ET is
the sum of water lost from the landscape through evaporation from the soil surface and
transpiration through the leaves of plants. ET is determined by the plant species and the
climatic conditions. By knowing the water storage capacity of a soil and the daily ET rate, you
can calculate when the available moisture will be near depletion and irrigation is needed. For
example, if a loam soil holds 38 mm of water in the top 30 cm, and during the summer the
ET rate is 6 mm per day, after 6 days (6 x 6.5 = 39) the available water would be depleted
and irrigation would be required. To replenish the soil moisture 38 mm of water would
need to be applied. This method is known as the ‘checkbook’ system of irrigation scheduling
and is simple, yet effective. As ET rates vary depending on climatic factors such as solar
radiation, temperature, humidity, wind speed, clouds, and fog, irrigation requirements also vary
accordingly. In the summers, ET reaches peak values while in the winter, ET is virtually zero;
but it increases during the spring with increased sunshine and temperature to a maximum in
midsummer.
GRIHA-speciic information
Objective
To reduce the landscape water requirements so as to minimize the load on the municipal water
supply and depletion of groundwater resources.
10.1 Commitment
10.1.1 Design the landscape so as to reduce water consumption by 30% or more (up to 50%).
Irrigate at the right time
Irrigate as infrequently as possible. Only when plants have used most of the available soil moisture
the next irrigation should begin. In general, irrigating once or twice a week is ideal. Irrigation timing
can be determined in two ways. The first method is to monitor the plants and/or soil in the landscape
or garden. The second method is to determine the amount of water that has been lost from the
landscape and how much will be needed to replace it.
Scheduling irrigation based on observation
Optimum irrigation requires irrigation just prior to water stress. However, if a little stress can be
tolerated, timing can be determined by careful observation of the landscape to notice the symptoms
of early water stress. Green lawn grass will begin to change from a bright green colour to a dull
colour when they become water stressed. They also lose their ability to spring back rapidly from foot
traffic, so a dry lawn will show visible footprints for a longer period of time. Another observation
method is to use indicator plants to predict irrigation needs. Almost every landscape has a shrub
or plant that wilts sooner than any other plant in the landscape. This plant can be used to indicate
the time to irrigate. Occasionally plants may wilt under hot, dry conditions even if the soil is moist.
Therefore, soil moisture should also be determined.
Scheduling irrigation based on evapotranspiration
Irrigation scheduling can also be determined by using evapotranspiration (ET) data. ET is
the sum of water lost from the landscape through evaporation from the soil surface and
transpiration through the leaves of plants. ET is determined by the plant species and the
climatic conditions. By knowing the water storage capacity of a soil and the daily ET rate, you
can calculate when the available moisture will be near depletion and irrigation is needed. For
example, if a loam soil holds 38 mm of water in the top 30 cm, and during the summer the
ET rate is 6 mm per day, after 6 days (6 x 6.5 = 39) the available water would be depleted
and irrigation would be required. To replenish the soil moisture 38 mm of water would
need to be applied. This method is known as the ‘checkbook’ system of irrigation scheduling
and is simple, yet effective. As ET rates vary depending on climatic factors such as solar
radiation, temperature, humidity, wind speed, clouds, and fog, irrigation requirements also vary
accordingly. In the summers, ET reaches peak values while in the winter, ET is virtually zero;
but it increases during the spring with increased sunshine and temperature to a maximum in
midsummer.
GRIHA-speciic information
Objective
To reduce the landscape water requirements so as to minimize the load on the municipal water
supply and depletion of groundwater resources.
10.1 Commitment
10.1.1 Design the landscape so as to reduce water consumption by 30% or more (up to 50%).
