Drip Irrigation Systems
When properly designed and managed, drip
irrigation has many advantages over other irrigation
methods, including: elimination of surface runoff,
high uniformity of water distribution, high water
usage efficiency, flexibility in fertilization, prevention
of weed growth and plant disease. Drip systems are
also easily integrated in fertigation systems and
automation.
Traditionally, irrigation water is applied to the entire
field, whether by sprinklers or by flood irrigation,
resulting in a significant loss of water. Drip irrigation
(or trickle irrigation) is a modern irrigation method
in which water is delivered directly into the root
zone of the plant.
This kind of system uses low pressure and low flow
rates and water is applied only to specific zones in
the field, where plants are grown. Typical drip
emitter flow rates are 0.6 - 16 L/hr (0.16-4.0 gal/
hr), and the most commonly used emitters are of
1-4 L/hr.

Number of drippers and their spacing
The main challenge in designing a drip irrigation
system is selecting the right combination of dripper
spacing, their total number and their required
discharge for a given soil and crop.
The two major factors that affect the selection of
the proper combination are the physical
characteristics of the soil and the water
requirements of the crop.
Drip emitters create different sub-soil wetting
patterns in different soil types.
The texture of the soil determines the vertical and
horizontal distribution of water in it.
In coarse textured soils (sandy soils) water will tend
to spread more vertically, while in fine textured
soils (clay soils) there will be a considerable lateral
movement, resulting in a larger radius of the wetted
zone.

Effect of soil type and drip emitter discharge
on water distribution
Q = Drip emitter discharge Q (1) > Q (2)
(Click image to enlarge)
Drip pattern
Therefore, spacing between drip emitters in sandy
soils should be smaller than in fine textured soils.
To get a uniform irrigation in row crops, spacing
between drip emitters should result in an overlap
between the wetted zones of each two drip
emitters.
Another factor affecting the radius of the wetted
zone is the emitter discharge.
The water requirement of the crop and the time
available for irrigation are used to determine the
number of emitters needed.

Example:
A 1.2 l/hr drip emitters were selected, the water
requirement of the crop is 3 l/day, irrigation
frequency is once in 4 days and time available for
irrigation is 2 hours.
Water amount needed per irrigation : 3 l/day/plant X
4 days = 12 liter/plant.
Irrigation rate required: 12 liter / 2 hours = 6 l/hr.
Number of drip emitters required: (6 l/hr) / (1.2 l/hr/
emitter) =
5 drip emitters per plant.

Fertilizer application through drip systems
Drip irrigation allows for flexibility in the application
of fertilizers, since fertilizers can be easily applied
through the irrigation water ( fertigation). This way
nutrients are delivered with the irrigation water,
directly to the active root zone of the plants.
Nutrients are supplied frequently at low
concentrations, to meet the plants' needs. It was
found that roots in the wetted area increase their
efficiency of water and nutrient uptake.
Therefore, selective wetting of the soil, as achieved
by drip irrigation, allows for savings both in water
and fertilizers. Drip irrigation can also reduce nitrate
losses due to leaching.

Irrigation and water content of the soil
Traditional irrigation methods are characterized by
high fluctuations in soil-moisture content, as high
quantities of water are applied at long intervals.
These fluctuations affect plant growth and crop
yields. Drip irrigation systems are able to supply
small amounts of water at high frequency intervals.
As a result, a relatively constant moisture level of
the soil can be maintained.
The optimal range of moisture in the soil can be
maintained at all times and managed more easily,
because water is applied in precise quantities on a
precise schedule, according to the crop
requirements. This promotes water saving, as well
as enhances growth and production.
In addition, the selective wetting prevents
evaporation of water from areas outside the wetted
zone.
Salinity Management in Drip Systems
If properly designed and managed, drip irrigation
allows for better salinity management, and a lower
salt content of the soil can be achieved, compared
with other irrigation methods.
Because water is applied at high frequencies and
the moisture content of the soil is relatively high,
the salt content of the soil is approximately similar
to that of the irrigation water.
In addition, fertilizers applied through the irrigation
water are much more diluted. The high frequency of
fertilizer applications, given at precise rates, can
prevent salt stress to the crop.
However, in drip irrigation salts tend to accumulate
close to the margins of the wetted zone, midway
between the drip emitters. The accumulated salts
may be washed by rain into the root zone of the
plants and cause salinity shock.
Salt accumulation at the top soil
Another problem that might occur is that during the
change of crops, the high concentration of salts at
the top soil may prevent the germination of new
seeds and damage young plants planted in the
regions of high salt concentrations.
Possible solutions to these problems are to design
the drip system with closely spaced emitters or
alternatively, leach the salts periodically, using a
sprinkler system.
source: http://www.smart-fertilizer.com/articles/drip-irrigation

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