Irrigation scheduling
Encyclopedia
Irrigation scheduling is the process used by irrigation
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...

 system managers to determine the correct frequency and duration of watering.

The following factors may be taken into consideration:
  • Precipitation rate of the irrigation equipment - how quickly the water is applied, often expressed in inches or mm per hour.
  • Distribution uniformity
    Distribution uniformity
    Distribution Uniformity or DU in irrigation is a measure of how uniformly water is applied to the area being watered, expressed as a percentage. The distribution uniformity is often calculated when performing an irrigation audit...

     of the irrigation system - how uniformly the water is applied, expressed as a percentage, the higher the number, the more uniform.
  • Soil infiltration rate
    Infiltration (hydrology)
    Infiltration is the process by which water on the ground surface enters the soil. Infiltration rate in soil science is a measure of the rate at which soil is able to absorb rainfall or irrigation. It is measured in inches per hour or millimeters per hour. The rate decreases as the soil becomes...

     - how quickly the water is absorbed by the soil, the rate of which also decreases as the soil becomes wetter, also often expressed in inches or mm per hour.
  • Slope (topography
    Topography
    Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...

    ) of the land being irrigated as this affects how quickly runoff
    Surface runoff
    Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...

     occurs, often expressed as a percentage, i.e. distance of fall divided by 100 units of horizontal distance (1 ft of fall per 100 ft (30.5 m) would be 1%).
  • Soil available water capacity
    Available water capacity
    Available water capacity or available water content is the range of available water that can be stored in soil and be available for growing crops....

    , expressed in units of water per unit of soil, i.e. inches of water per foot of soil.
  • Effective root
    Root
    In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

    ing depth of the plants to be watered, which affects how much water can be stored in the soil and made available to the plants.
  • Current watering requirements of the plant (which may be estimated by calculating evapotranspiration
    Evapotranspiration
    Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...

    , or ET), often expressed in inches per day.
  • Amount of time in which water or labor may be available for irrigation.
  • Amount of allowable moisture stress
    Moisture stress
    Moisture stress occurs when the water in a plant's cells is reduced to less than normal levels. This can occur because of a lack of water in the plant's root zone, higher rates of transpiration than the rate of moisture uptake by the roots, for example, because of an inability to absorb water due...

     which may be placed on the plant. For high value vegetable
    Vegetable
    The noun vegetable usually means an edible plant or part of a plant other than a sweet fruit or seed. This typically means the leaf, stem, or root of a plant....

     crops, this may mean no allowable stress, while for a lawn
    Lawn
    A lawn is an area of aesthetic and recreational land planted with grasses or other durable plants, which usually are maintained at a low and consistent height. Low ornamental meadows in natural landscaping styles are a contemporary option of a lawn...

     some stress would be allowable, since the goal would not be to maximize production, but merely to keep the lawn green and healthy.
  • Timing to take advantage of projected rainfall
  • Timing to take advantage of favorable utility rates
  • Timing to avoid interfering with other activities such as sporting events, holidays, lawn maintenance, or crop harvesting.


The goal in irrigation scheduling is to apply enough water to fully wet the plant's root zone while minimizing overwatering and then allow the soil to dry out in between waterings, to allow air to enter the soil and encourage root development, but not so much that the plant is stressed beyond what is allowable.

In recent years, more sophisticated irrigation controllers have been developed that receive ET input from either a single on-site weather station or from a network of stations and automatically adjust the irrigation schedule accordingly. When properly set up and maintained, these controllers do tend to conserve water over conventional human scheduling as the program is updated at least daily. However ET figures do not always match with the water crops actually use, for an accurate system you need to incorporate actual soil moisture data from a good quality capacitance sensor such as those in a SENTEK ENVIROscan or Diviner 2000 probe see www.sentek.com.au http://www.sentek.com.au. [1]

Other devices helpful in irrigation scheduling are rain sensors, which automatically shut off an irrigation system when it rains, and soil moisture sensing devices such as capacitance sensors, tensiometers and gypsum blocks.

For more information and advice on irrigation scheduling see www.irrigationworld2000.com http://www.irrigationworld2000.com

See also

  • Frequency domain sensor
    Frequency domain sensor
    Frequency domain sensor is an instrument developed for measuring soil moisture content. The instrument has an oscillating circuit, the sensing part of the sensor is embedded in the soil, and the operating frequency will depend on the value of soil's dielectric constant.There are two types of...

  • Neutron probe
    Neutron probe
    A neutron probe is a device used to measure the quantity of water present in soil.A typical neutron probe contains a pellet of americium-241 and beryllium. The alpha particles emitted by the decay of the americium collide with the light beryllium nuclei, producing fast neutrons...

  • Nonlimiting water range
    Nonlimiting water range
    The Non-limiting water range represents the range of water content in the soil where limitations to plant growth are minimal...

  • Time Domain Reflectometer
  • Irrigation in viticulture
    Irrigation in viticulture
    The role of irrigation in viticulture is considered both controversial and essential to wine production. In the physiology of the grapevine, water is a vital component to function of the vine with its presence or lack impacting photosynthesis, new plant shoot growth, as well as the development of...

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