DRIP IRRIGATION

UNDERSTANDING THE BASICS

DRIP IRRIGATION SYSTEM OVERVIEW

Irrigation is the watering of land by artificial methods. Without irrigation, agriculture is limited by the availability and reliability of naturally occurring water from floods or rain. Drip irrigation is widely accepted as the most efficient irrigation technique as it allows high uniformity of water and nutrient application


A drip irrigation system comprises many components, each one of them playing an important part in the

operation of the system.

The aim of this chapter is to provide an overview of the drip irrigation system components, their functions

and properties.

OTHER IRRIGATION SYSTEMS:

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DRIP IRRIGATION SYSTEM LAYOUT

Water source

There are basically two main types of water sources: groundwater and surface water:

Many existing and potential water supply sources for irrigation systems are derived from surface water,

which does not tend to have high levels of salts (with the exception of some coastal areas), and thus

systems are usually less prone to the formation of precipitates in drippers when using a surface water source.

Surface water, however, tends to introduce biological hazards. If wastewater is being considered as a

source, quality and clogging potential will vary depending upon the extent of treatment.

Groundwater is generally of higher quality than surface water. However, iron and manganese levels should

be measured, as high levels may lead to dripper clogging, and treatment may be required.

Pumps & pumping stations

Unless the water at the source is supplied at an adequate flow rate and pressure (by municipal or other

entity supply, a pre-existing pump upstream from the irrigation system or gravitational pressure*), a pump

will be needed to push water from the source through the pipes and drippers.

Most irrigation systems include pumps as an integral part of the drip irrigation system.

*Gravitational pressure (also known as hydrostatic pressure) is the pressure at a point in a fluid at rest

due to the weight of the fluid above it. If the water source is at a higher elevation than the drippers in the

field, the elevation difference between them will determine the gravitational pressure in the system

(e.g. the water level in a tank is 5 meters above the elevation of the pump's axis, the gravitational pressure

is 5 meters = 0.5 bar = 7.25 PSI).

Selecting a pump for an irrigation system requires an understanding of the water conditions and local

system requirements.

Poor pump selection can lead to high operating costs and shortened pump life; this in turn impacts on the

performance and reliability of the whole irrigation system.

When a pump site is selected it is necessary to consider a range of factors, including availability of power,

proximity to the development site and water quality issues.


Power source for the pump


The power source for the pump will depend on the availability and accessibility of the energy resource in

the local area.

In most instances, electricity is preferred because of reduced labor requirements and higher efficiency,

resulting in lower energy cost. Three-phase power is usually required to operate over 10 horsepower (hp)

irrigation pumps.

If electricity is not available, alternative power sources such as diesel, gasoline, or solar may be used. The

most common alternatives are gasoline engines for small pumps and diesel engines for larger pumps.

PUMP MACHINERY SYSTEM

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Filtration

Filtration is critical in any drip irrigation system. Effective filtration is essential for proper irrigation system

operation and long-term performance, as it prevents the irrigation water from clogging the drippers.


Water quality


The concept "water quality" relates to the variety and concentration of the dissolved and suspended

components in the water.


Water requirements for drip irrigation


The quality of water for irrigation relates to the parameters required to maintain the crop's health and the

integrity of the irrigation system. Every type of pressurized irrigation system requires attention to the

water quality to avoid clogging of the irrigation components in order to enable orderly long-term irrigation

according to the irrigation program.

Water quality will dictate filtration requirements, chemical injection requirements, and management of the

irrigation systems to prevent dripper clogging.

Causes of dripper clogging in systems may be chemical (precipitates or scale), physical (grit or particulates

such as sand and sediment) or biological (such as algae or bacteria).

The water’s chemical characteristics are influenced by the variety and concentration of the substances

dissolved in it. These dissolved substances include ions of dissolved salts such as chloride, sodium and

nutrients (nitrogen, phosphorous, potassium and others). Calcium and magnesium influence the hardness

of the water, iron and manganese are liable to be found either dissolved or as a residue, along with other

dissolved organic compounds and even poisonous substances.

The biological characteristics of the water quality include a variety of living organisms such as microorganisms, including bacteria, viruses, single celled entities, algae and zooplankton, which develop in open

water along with creatures developing within the water transport system itself.

The water quality is expressed by the physical conditions and the variety and concentration of its

constituents.

The quality of the water is determined by a wide variety of parameters (measured or calculated)

affecting the crop, the soil and the irrigation system. Some of them are listed below:

EC (electrical conductivity)

pH (level of acidity or alkalinity)

Ca (calcium - hardness of the water)

Mg (magnesium)

Na (sodium)

K (potassium)

HCO3 (bicarbonate)

CO3 (carbonate)

Alk (alkalinity)

Cl (chloride)

SO4 (sulfate)

PO4 (phosphate)

N-NH4 (nitrogen-ammonium)

N-NO3 (nitrogen-nitrate)

B (boron)

Fe (iron)

Mn (manganese)

TSS (total suspended solids)

TDS (totally dissolved solids)

Turbidity

Algae and Chlorophyll

Zooplankton

BOD (biochemical oxygen demand*)

COD (chemical oxygen demand*)

VSS (volatile suspended solids)

*When waste, industrial effluent and/or recycled waters are used.