Irrigation Scheduling Concept

Irrigation scheduling is essential for good water management and it deals with two classical questions related to irrigation. These are-

(1) how much to irrigate and

(2) How often to irrigate.

How often and how to irrigate is function of irrigation water needs of the crop. For example, if irrigation water need of crop is 5 mm/day, each day crop needs a water layer of 5 mm over the whole cropped area.

However, 5 mm of water need not be supplied every day. Generally, drips irrigation systems are designed to meet irrigation water requirement on daily or at an interval of 2-3 day days. However, longer gap between irrigations is maintained in other irrigation system. In any case, irrigation interval is chosen such that crop does not suffers from water tress.

In many cases irrigation scheduling is performed based on the irrigator’s personal experience, plant appearance, watching the neighbor, or just simply irrigating whenever water is available. However, over the year a number of irrigation scheduling techniques based on soil water monitoring, plant monitoring and water balance approach have been developed. 

Advantages of Irrigation Scheduling

Irrigation scheduling offers several advantages:

  • It enables the farmer to schedule water rotation among the various fields to minimize crop water stress and maximize yields.
  • It reduces the farmer’s cost of water and labouras it minimizes thenumber of irrigations.
  • It lowers fertilizer costs by holding surface runoff and deep percolation (leaching) to a minimum.
  • It increases net returns by increasing crop yields and crop quality.
  • It minimizes water-logging problems by reducing the drainage requirements.
  • It assists in controlling root zone salinity problems through controlled leaching.
  • It results in additional returns by using the “saved” water to irrigate non-cash crops that otherwise would not be irrigated during water-stress periods.

Full Irrigation

It provides the enough water to meet the entire irrigation requirement and is aimed at achieving the maximum production potential of the crop. Excess irrigation may reduce crop yield because of decreased soil aeration.

Deficit Irrigation

It means partially meeting the crop water requirement. It is practiced when there is water scarcity or the irrigation system capacity is limited. With deficit irrigation root zone is not filled to the field capacity moisture level.

Deficit irrigation is justified in case where reducing water application below full irrigation causes production cost to decrease faster than revenue decline due to reduced yield. This method allows plant tress during one or more periods of growing season.

However, adequate water is applied during the critical growth stages to maximize water use efficiency. Critical growth stage of some the crops are shown in the following Table-

Critical growth stages for managing water use efficiency

Crop Growth period Most sensitive to water  Stress Growth Interval in which irrigation Produces Greatest Benefits
Sorghum Boot- heading Boot- soft dough
Wheat Boot- flowering Jointing- soft dough
Corn Tassel- pollution 12 leaf- blister kernel
Cotton First bloom- peak bloom First bloom- boils well- formed
Dry beans Flowering –early  podfill Axillary bud- podfill
Potatoes Tuberization Tuberization- maturity
Soybean Flowering- early podfill Axillary bud- podfill
Sugarbeets No critical stages WUEis maximized when water depletion is limited ton about 50% available water depletion

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