💧 Irrigation: Timing and Methods

Rainfall rarely arrives exactly when crops need it. Irrigation exists to fill that gap. But good irrigation is not simply adding water. It means giving the right amount of water, at the right time, by the right method, while also avoiding waterlogging and root-zone damage.

---

What is irrigation?

Irrigation is the artificial application of water to the soil for crop production in addition to rainfall and groundwater contribution.

Its practical purpose is to:

• support crop growth when rainfall is insufficient
• stabilize yield
• improve productivity under controlled management

Irrigation becomes especially important where rainfall is:

• low
• uncertain
• unevenly distributed

---

Why water is essential to plants

Water is one of the most important requirements of crop growth.

Its major roles include:

• maintaining plant turgidity and keeping plants erect
• forming an essential part of protoplasm
• regulating plant temperature
• meeting transpiration requirement
• dissolving and transporting soil nutrients
• participating in photosynthesis

Water is not just a supporting input. It is directly involved in plant structure, nutrient transport, temperature control, and food production inside the crop.

---

Time of irrigation and the optimum soil-moisture range

Crops use water from the moisture stored in the soil. If soil moisture becomes too low, crop demand is not met. If too much water is present, soil air decreases and plant growth suffers.

So, crops grow best within an optimum soil-moisture range.

Upper and lower useful limits

The upper limit is the field capacity, usually around:

• -0.01 to -0.03 MPa

The lower critical limit is just above the permanent wilting point, around:

• -1.5 MPa

The aim of irrigation is to keep soil moisture within this useful range.

What happens after irrigation?

Immediately after irrigation:

• macro-pores and micro-pores may fill with water
• water in macro-pores drains downward within about 48 hours
• water in micro-pores remains available to plants

As soil dries by evaporation and transpiration:

• crops may show temporary daytime wilting
• they may recover at night at first
• if the condition continues, persistent wilting develops

This stage tells the farmer that irrigation should not be delayed too far.

---

Criteria for choosing an irrigation method

No single irrigation method suits all fields.

Method selection depends on:

• water source
• topography
• amount of water to be applied
• crop type
• cultivation method
• soil infiltration behaviour

This is why rice, sugarcane, vegetables, orchards, and dryland crops are not all irrigated in the same way.

---

Main irrigation methods

The source groups irrigation methods into three broad classes:

1. surface irrigation
2. sub-surface irrigation
3. pressurized irrigation

---

Surface irrigation

Surface irrigation is the oldest and still the most common method.

It is most suitable for:

• relatively level lands
• low to moderate infiltration rates
• gentle slopes

The major forms include:

• border irrigation
• check basin irrigation
• furrow irrigation

Border irrigation

In border irrigation, the field is divided into long parallel strips separated by low ridges. Water is released at the upper end and flows downward as a sheet.

Suitable for:

• moderately low to moderately high infiltration soils
• close-growing crops such as wheat, barley, fodder crops, and legumes

Advantages:

• simple construction
• reduced labour compared with conventional basin systems
• good water distribution
• good drainage if outlets are present

Not ideal for:

• very coarse sandy soils
• very heavy soils with extremely low infiltration
• rice in usual practice

Check basin irrigation

Here, the field is divided into small, nearly level basins surrounded by bunds. Water is retained until it infiltrates.

Suitable for:

• gentle slopes
• moderate to low infiltration soils
• many grain and fodder crops

Advantages:

• useful where salt leaching is needed
• reduces erosion
• allows high application efficiency

Limitations:

• bunds interfere with implements
• more labour is needed
• more land is lost in ridges and channels
• not suitable for crops sensitive to wet soil around the stem

Furrow irrigation

Furrow irrigation is used mainly for row crops. Water flows through furrows between crop rows and moves laterally into the root zone.

Suitable for:

• maize
• sorghum
• sugarcane
• cotton
• tobacco
• groundnut
• potato

Advantages:

• only part of the soil surface is wetted
• labour requirement is reduced
• less land is wasted than in some basin systems

Types include:

• all-furrow irrigation
• alternate-furrow irrigation
• skip-furrow irrigation

Surge irrigation

Surge irrigation means applying water intermittently in ON and OFF cycles through furrows.

Benefits:

• faster water-front advance
• reduced infiltration loss during later surges
• more uniform soil-moisture distribution
• irrigation efficiency can be high

---

Sub-surface irrigation

In sub-surface irrigation, water is supplied below the soil surface by maintaining an artificial water table, usually about 30 to 75 cm below the ground surface.

Moisture then moves upward by capillary action.

Advantages:

• minimum surface evaporation loss
• no surface land wastage
• no interference with machinery
• cultivation can continue without disturbance from irrigation water on the surface

Disadvantages:

• high cost
• danger of waterlogging
• possible pipe choking
• requires special soil and field conditions
• good-quality water is necessary

---

Pressurized irrigation

Pressurized irrigation systems deliver water through pipes under pressure.

The source emphasizes modern systems such as:

• sprinkler irrigation
• drip irrigation

Sprinkler irrigation

In sprinkler irrigation, water is sprayed into the air and falls on the field like rainfall.

It may be arranged through:

• rotating-head systems
• perforated-pipe systems

By portability, systems may be:

• portable
• semi-permanent
• solid-set
• permanent

Advantages:

• suitable for undulating lands
• saves water compared with many surface methods
• fertilizer and chemicals can be applied through irrigation water
• reduces erosion
• suits coarse-textured soils
• can help in frost protection and temperature moderation
• saves land otherwise lost in channels

Limitations:

• high initial cost
• wind reduces efficiency
• evaporation loss may be higher
• not ideal for tall crops like sugarcane
• not suitable for heavy clay soils
• poor-quality water may clog nozzles or harm sensitive crops

Drip irrigation

Drip irrigation, also called trickle irrigation, applies water slowly and directly near the root zone.

Its major agronomic logic is:

• high water-use efficiency
• minimum evaporation and runoff
• precise irrigation near active roots

It is especially useful in:

• orchards
• vegetables
• wide-spaced crops

Drip systems are now central to micro-irrigation because they conserve water and allow precise nutrient application.

---

Why drainage is linked with irrigation

Irrigation and drainage go together. Irrigation supplies water, while drainage removes excess water from the root zone.

Drainage is the artificial removal of excess surface or subsurface water beyond the quantity required by the crop.

Role of drainage

Good drainage helps by:

• improving aeration
• allowing oxygen to enter the root zone
• helping carbon dioxide and harmful gases escape
• improving activity of aerobic organisms
• reducing iron and manganese toxicity in acid soils
• allowing deeper root growth
• helping soil dry to workable condition
• preventing salt build-up in upper soil layers

Too little water reduces crop growth, but too much water also reduces crop growth. Irrigation without drainage can therefore become harmful.

Summary Cheat Sheet

Topic	Key Point
Irrigation	Artificial application of water to supplement rainfall for crop production.
Why crops need water	Water supports turgidity, nutrient transport, transpiration, and photosynthesis.
Optimum moisture range	Irrigation aims to keep soil moisture between field capacity and the permanent wilting limit.
Surface irrigation	Includes border, check basin, furrow, and surge methods.
Border irrigation	Best for close-growing crops on suitable leveled land with moderate infiltration.
Check basin irrigation	Water is retained in small basins; useful for many crops and salt leaching.
Furrow irrigation	Common for row crops; water flows between rows and wets the root zone laterally.
Sub-surface irrigation	Water supplied below ground by maintaining a shallow water table.
Sprinkler irrigation	Pressurized system useful on uneven land and coarse soils, but costlier and wind-sensitive.
Drip irrigation	Precise root-zone application with high water-use efficiency.
Drainage	Removal of excess water to improve aeration, root health, and salt control.

References

1 source • [1]

[1]

ICAR e-Courses