Meaning and Importance of Irrigation in Crop Production

Irrigation is the artificial application of water to crops for the purpose of providing the moisture required for their growth. An adequate water supply is important for crop development, and the quantity required varies depending on the type of crop and should be met for optimal production.

Various methods can be used to supply irrigation water, and each method has its advantages and disadvantages which should be considered when selecting the one most suited to local conditions.

This article explains the different methods or systems of irrigation used to apply water to crops.

Functions and Components of Irrigation Systems

The principal function of an irrigation system is to supply water to crops in the quantity and at the time it is needed. Specific functions include diverting water from the source, conveying it to individual fields within the farm, distributing it within each field, and regulating the flow.

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Types of Irrigation Systems Used in Agriculture

There are several ways of directing, conveying, and applying irrigation water on the farm.

1. Water Diversion Methods in Irrigation Systems

There are two primary ways of diverting surface and underground water:

i. Gravity method: Water is admitted from an open water source into farm channels and pipelines by gravity.

ii. Pump method: This involves the use of centrifugal pumps to divert water from the source. The power sources used are usually electric motors or internal combustion engines.

2. Water Conveyance Methods in Irrigation Systems

Water is conveyed from the source to cropped areas on the farm using networks of open channels or pipelines. Open channels may be lined or unlined, and pipelines may be partially open to the atmosphere or pressurized.

i. Open Channels: These are usually graded in the direction of flow and may be lined or unlined. They are used with both surface and groundwater sources and farm application systems.

Channels are lined with hard surfaces such as concrete, asphalt, or soil sealants to reduce maintenance costs, channel size, and seepage losses through the bed and walls. Unlined ditches are used due to their low capital cost and ease of construction and demarcation.

ii. Pipelines: On the farm, pipe networks are classified as open (low head) or closed (pressurized), depending on whether the system is open to the ground surface or buried. Surface pipelines can be placed below the tillage zone to minimize damage from machinery.

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Irrigation Water Application Systems in Agriculture

Application systems refer to how irrigation water is directly applied to crops. These systems vary based on soil and subsoil types, topography, nature of the water supply, farm size, and crop type. The three major application systems include:

1. Surface irrigation system

2. Sprinkler irrigation system

3. Drip or trickle irrigation system

1. Surface Irrigation System

Surface irrigation involves the application of water using gravity flow over the surface of the field. The entire field may be flooded (basin irrigation), or water may be fed into small channels (furrows) or strips of land (borders).

i. Basin Irrigation: Basins are flat areas of land surrounded by low bunds that prevent water from flowing into adjacent fields. Basin irrigation is commonly used for rice grown on flat land or terraces on hillsides.

Trees can also be planted in basins, with each tree located in its own basin. This method is suitable for crops that are not affected by standing water for long periods.

ii. Furrow Irrigation: In this system, water flows through furrows (spaces between ridges) and gradually wets the ridges. It is used on gently sloped land to avoid erosion and is ideal for crops grown on ridges.

iii. Border Irrigation: This method divides a field into long, narrow plots using low bunds that extend along the slope. The bed of each plot is level from side to side, and water flows down the slope guided by the bunds. The strip size and water quantity depend on soil type and crop.

Surface irrigation systems generally require lower initial investment (except where land leveling is extensive), are more labour intensive, and apply water less efficiently compared to other systems.

They are best suited to soils with moderate to low infiltration capacity and land with uniform terrain and slopes less than 2%.

2. Sprinkler Irrigation System

Sprinkler irrigation mimics natural rainfall. Water is pumped through a pipe system and sprayed onto crops using rotating sprinkler heads.

This system is efficient but has a relatively high capital cost, low labour requirement, and uses more energy than other methods. It is suitable for:

i. Permeable soils that are difficult to irrigate using other methods

ii. Areas with shallow soils and terrain unsuitable for leveling

iii. Land with steep slopes and easily erodible soil

iv. Undulating terrain where leveling is costly

Sprinkler systems are also useful for frost protection, applying fertilizers and chemicals, controlling wind erosion, cooling crops and soils, delaying fruit and bud development, and seed germination.

3. Drip or Trickle Irrigation System

Drip irrigation involves the frequent, slow application of water directly onto the land surface or into the root zone of crops. It focuses on irrigating only the crop’s root zone and maintaining optimal moisture levels.

Water is conveyed under pressure through a pipe system and slowly dripped onto the soil through emitters or drippers placed near the plants.

Drip irrigation is adaptable to most soil types and terrains and is highly suitable for high-value crops. It is the most efficient irrigation system.

For effective and efficient use of irrigation water, it is important to understand the different systems, the soil type, the land's topography, and the type of crop grown.

This helps in selecting the irrigation system that best suits the crop, minimizes water wastage, and enhances efficient water use.

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