Subsurface Drip Irrigation and IWM

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Subsurface Drip Irrigation (SDI) is one of several types of
Microirrigation (Conservation Practice Standard 441). It is a planned
irrigation system in which water is applied directly to the root zone of
plants by means of applicators (E.g. orifices, emitters, and porous
tubing) placed below the ground surface. It is operated under low
pressure. It is one of the more advanced irrigation methods in use
today. It is potentially more efficient than flood or sprinkler
irrigation, due, in large part to reduced evaporation.

Basic requirements: An operational SDI system involves a pressurized
water distribution system and includes a variety of components such as
pumps, valves, filters, chemical injectors and a distribution system of
solid pipes and flexible tape or tubes.

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**[Advantages:]{.underline}**

SDI has gained attention during recent years. SDI systems can apply
water and nutrients directly to individual plants or trees, reducing the
wetted surface area to a fraction of other types of irrigation systems.

-   SDI is a low pressure, low volume irrigation system suitable for
    high return value crops such as vegetable and nut crops.

-   If managed properly, it can increase yields and decrease water,
    nutrient, pesticide, and labor requirements.

-   SDI applies water to the plant's root zone reducing evaporation
    losses.

-   Weed growth is reduced.

-   It has a high distribution uniformity allowing for high application
    efficiency.

-   SDI can irrigate sloping or irregularly shaped land areas that
    cannot be flood irrigated.

-   There is no runoff which results in reduced soil erosion or wasted
    water.

-   Limited deep water drainage (with proper scheduling -- management).

-   High Fertilizer efficiency: Fertilizer is applied directly to root
    area and can be applied at any time and any dosage without wetting
    plant foliage. Any water soluble fertilizer may be injected through
    a SDI system.

-   Yields are typically increased. Soil moisture and fertility in root
    zone can be maintained at optimum levels.

-   Fewer tractor passes through field

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**[Disadvantages:]{.underline}**

As with other irrigation methods, concerns arise and SDI is no
exception. Some concerns include initial system cost, power cost,
emitter uniformity, system hygiene, longevity, fertility, maintenance,
germination, crop performance, and rotation into other crops.

-   SDI requires a heavy initial investment. Presently, initial start up
    cost is between \$1,200 and \$1,500 per acre. As an example,
    amortizing a loan at 8% interest rate over a 10 year period amounts
    to 22% of the initial investment that must be recovered every year.
    This, along with other costs, has to be compared to the benefits.

-   As with anything, there is always apprehension about the decision to
    convert to a something different. A sizeable personal effort is
    required to understand the anticipated outcome as well as the
    operation and maintenance of a SDI system.

-   SDI requires a higher skilled labor than most other irrigation
    systems.

-   The systems must be carefully designed to ensure proper emitter and
    row spacing for the crop grown.

-   Maintenance of the system must be performed in order to ensure the
    investment for the planned service life of the system.

-   Soil salinity issues must be addressed as well as the effects of
    excess calcium carbonate dissolved in the irrigation waters.

-   Filtration is critical. Emitter clogging will affect distribution
    uniformity. Algae growth and scale build up (CaCO3) must be
    controlled. As with all systems that use filters, provisions must be
    made for utilizing the flush water.

-   Components can be easily damaged by vandals, rodents, or equipment
    operator error.

-   Few pesticides are available for injection.

-   Water must be available on a regular basis.

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**Micro Irrigation Methods for SDI and Other Systems**

Micro-irrigation can be the most water efficient of all systems. The
irrigator has a high degree of control over the way water is applied.
These systems must be designed, installed, operated, and maintained
carefully. Systems are prone to clogging and need clean water. Water
applications are so light and frequent but can be operated to ensure a
full root zone. ***Soil moisture must be managed carefully throughout
the season.***

[Point source emitters]{.underline}:

The numerous emitters available apply water in drops or trickles, spray
or mist (micro-sprinklers), or small fountains (bubblers). Emitters are
generally placed in or along polyethylene tubing and dissipate water
pressure through the use of long paths, small orifices, or diaphragms.
Some emitters are pressure compensating, designed to discharge at a
nearly constant rate over a range of pressures. Most drip emitters are
designed to be used above ground.

[Line Source emitter systems (Also known as drip tape or
tubing):]{.underline}

Line source emitters are basically flexible tubing with uniformly spaced
emitter points. Some drip tape emits water through small laser drilled
holes. Other drip tape designs (turbulent flow tape) include equally
spaced tortuous path emitter devices within the tubing. Some drip tape
is designed for above ground use, while other types may be buried.

[Basin Bubblers:]{.underline}

Basin bubblers apply water in a small basin or depression in the
surrounding soil holds the water to allow infiltration. Basin bubbler
systems are more applicable in orchards.

[Spray or Mini-Sprinklers:]{.underline}

Spray or mini-sprinkler systems emit droplets from small, low pressure
heads. Some micro-sprinklers have spinners, while others contain no
moving parts. These systems cover a wider area than most drip emitters,
with a typical wetting diameter of two to seven feet. Mini-sprinklers
are less prone to clogging than point source emitters.

Typical systems in the southwest utilize groundwater, although surface
water can be used.

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> The following pictures show a typical SDI system. - Luna County

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**Design Requirements for Subsurface Drip Irrigation - Irrigation
System, Microirrigation (441):**

An irrigation system for distribution of water directly to the plant
root zone by means of surface or subsurface applicators.

This practice will be designed in accordance with all federal, state and
local laws and ordinances. Micro irrigation Systems shall consist of
acceptable pipe design and layout to distribute the water in a uniform
manner for the intended life of the practice. Resource inventories,
local conditions and the intended use will need to be assessed for the
proposed Micro irrigation System design and location. A Micro irrigation
System design will be developed with the client that meets the intended
goals and objectives. All materials shall be of high quality. All
appropriate job sheets, maps and reports must be developed with
landowners input, review and concurrence (See Practice Standard,
Specification and Job Sheet 441).

The important components of a drip irrigation system include a water
source, pump, backflow preventer, injector, filter, pressure regulator,
valves, and a distribution system of pipes (main and submain lines) and
tubes (laterals). Solenoid valves and a controller can be used to
automate a system.

The minimum system capacity shall be adequate to deliver the average
daily water requirement during the peak use month in not more than 18
hours of operation. The system design capacity shall be adequate to meet
the intended water demands during the peak use month for all plants
planned to be irrigated in the design area. Design capacity shall
include an allowance for reasonable water losses (evaporation, runoff,
leaching requirements, and deep percolation).

Determine the volume of water available and the maximum flow rate of
that water. Currently most SDI system are being planned and designed by
private contractors. The following information sheet is what the SW Area
Engineer is requesting that the contractors provide upon review
approval.

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  ---------------------------------------- ------------------------------
  **Design Area (Plan Map)**               **Submain/manifold**

  Producers Name                           **All Calculations & Input**

  Structure locations, well locations      per block
  (water supply location)                  

  Dimensions -- elevations - slopes -      pressure rating & pressure in
  scale                                    pipe

  Block Layout                             type (diameter, type, etc)

  North Arrow                              length (from mainline to
                                           lateral total lengths of
                                           lateral)

  Water source and available Q             layout (location)

  Location of Pressure relief & air relief show lateral location
  valves                                   

  Location of all appurtenances            Velocity & Q

  Crops                                    **Laterals**

  Cu of crops                              **All Calculations & Input**

  How many blocks will be irrigated        \# laterals / block
  simultaneously                           

  how much time to irrigate each block or  spacing
  set                                      

  Maximum velocity 5 fps in pipeline       type of drip tape - size,
                                           weight, etc

  **Drip System (Design)**                 emitter spacing

  **All Calculations & Input**             Emitter flow rate @ \_\_ psi
                                           according to manufacturer

  Filter System                            emission uniformity

  System Q                                 distribution uniformity

  Capacity of filter & requirements of     Total Q per lateral & block
  filter                                   

  Chemigation-injection                    **Flush lines**

  All appurtenances required (well,        **All Calculations & Input**
  filter, flushing, shutoff valves, air    
  relief etc.)                             

  pressure @ filter inlet                  flows (Q)

  pressure @ filter outlet                 how many laterals attached to
                                           flush line

  pump pressure                            type (diameter, type, etc)

  All pipelines to be installed to NRCS    lengths
  standards (depths, velocity, psi, etc.)  

  **Mainline**                             layout

  **All Calculations & Input**             

  Is mainline pressure same as pressure @  
  filter outlet                            

  velocity & Q                             

  type (diameter, type, etc)               

  pressure rating & pressure in pipe       

  Layout                                   

  show submain locations- direction of     
  outlet flow                              
  ---------------------------------------- ------------------------------

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**Maintenance of Micro Irrigation Systems**

Water quality is a factor in maintaining micro irrigation systems. A
water quality test will measure silt or sand; algae; bacteria; dissolved
solids such as iron, sulfur, salts, and calcium; and the pH of the
water. For additional information on system maintenance, contact the
equipment manufacturer.

**[Maintenance tasks:]{.underline}**

Annually treat system with acid to neutralize calcium carbonates if the
water is "hard". Consult equipment manufacturer for type of acid and
treatment interval.

**[Regularly:]{.underline}**

-   Irrigation system evaluation by a trained professional is highly
    recommended.

-   Check for leaks, rodent damage, and mechanical damage.

-   Inspect pressure regulating valves and pressure gauges for correct
    operation and pressure readings. Liquid filled pressure gauges are
    recommended.

-   Flush lateral lines. Depending on water quality and filtration
    system, flushing should be done bi-weekly and after fertilizer or
    chemical injection or chlorination.

-   Regularly check for and clean or replace clogged emitters. Drip
    emitters that are only partially clogged are difficult to identify
    without catching the flow to determine the discharge rate.

-   Check emitters for correct flow. Take precise measurements at least
    twice each year by catching the flow from several emitters in a
    calibrated cylinder (such as a rain gauge) during a carefully timed
    interval.

-   Backwash filters either manually or using automatic cycle, depending
    on system design and type of filter.

-   Replace cartridge filters.

-   If filter media (such as sand) cakes, replace media. For sand
    filters, periodically supplement with additional media.

-   Chlorinate system with 10 ppm if water has high organic load.

-   If clogging due to organic matter continues to be a problem, inject
    50-100 ppm of chlorine and allow to sit for 24 hours.

-   If clogging due to precipitates (such as calcium carbonate)
    persists, inject system with acid to lower pH to about 5. Allow to
    sit for 24 hours. Contact equipment manufacturer before undertaking
    this task to determine the minimum pH allowable for system type.

**[At Season Shutdown:]{.underline}**

-   Treat entire system with 40 ppm residual chlorine concentration for
    at least four hours, and completely flush the system.

-   Drain water from all pipelines. The system may have to be blown out
    lateral by lateral with an air compressor to accomplish this. Don't
    exceed 15 to 20 psi of air pressure, or you'll blow off the
    emitters. Polyethylene pipes can withstand some freezing without
    breaking, so it isn't critical that all water be removed. In cases
    where freezing may be a problem, add non-toxic antifreeze (type used
    in RV's) to the piping system and distribute it throughout with
    compressed air.

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**Efficiency of Micro-Irrigation systems (SDI)**

Application efficiency, which is the percentage of applied water
beneficially used by the crop can approach 100% for SDI. High efficiency
is also realized with fertilizer application using SDI. Injected
fertilizer (fertigation) is applied directly to root area and can be
applied at any time and any dosage without wetting plant foliage.

Properly designed systems are highly efficient in their use of water and
energy. Below are a few suggestions for ensuring that the system is
running efficiently:

Make sure you know your exact field size. It's common to overestimate
field size, leading to overestimating water requirements. This concern
is commonly taken care of by proper planning, design, and monitoring of
the soil moisture.

Avoid excessive back flushing that wastes water and energy and creates a
water disposal problem. Measure back flushing amounts.

Find and address causes of plugging. Investigate the source and fix the
plugging problem.

Check for plugged filter screens. Undo and clean any screens that are
plugged.

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**Scheduling Irrigations -- The Irrigation Requirement:**

To effectively schedule irrigations, you must know:

-   The flow rate of each emitter

-   The crop (or plant) canopy area

-   An estimate of the plant's daily water-use (evapotranspiration or
    ET)

[The equation used to estimate the irrigation requirement (IR) per Plant
is:]{.underline}

IR = (0.623 x CA x Plant Factor x ETr) / IE

Where:

IR = the irrigation requirement in gallons

0.623 = gallons of water required to fill 1 square foot 1 inch deep

CA = plant canopy area in square feet

Plant factor = 0.85 for tomatoes, chili, and sweet corn (may be higher
for melons, squash, cucumbers, etc.)

ETr = reference ET (refer to Irrigation water requirements by local/crop
data)

IE = irrigation efficiency (assume 90% for SDI)

[Calculating the Crop Canopy Area:]{.underline}

Area of a circle = d2 x 0.785 (diameter x diameter x 0.785)

Example: plant diameter = 18 inches or 1.5 ft.

Area = 1.5 x 1.5 x 0.785 = 1.77 sq. ft..

[EXAMPLE: Scenario]{.underline}

Location -- Albuquerque

Date -- May 25 (ETr = 0.41 inch)

Chile plant (plant factor = 0.85)

Measured (circular) plant diameter = 1 foot

Estimated irrigation efficiency (IE) = 90 % or 0.9

Calculations: CA = 1 x 1 x 0.785 = 0.785

IR = (0.623 x 0.785 x 0.85 x 0.41)/0.9 = **0.19 gallons** (24 fluid
ounces) per plant per day

**NOTE: There is no substitute for frequently checking the moisture in
the soil profile.**

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**Water Quality and SDI systems:**

The irrigation water to be used in a drip system should be evaluated
carefully to assess any potential clogging problems. Materials suspended
in the water, such as sand, silt, and algae, can block emitter flow
passages or settle out in the drip lines. Other contaminants, such as
calcium, bicarbonate, iron, manganese, and sulfide, can also precipitate
to clog emitter flow passages.

All water needs to be tested to determine levels of dissolved salts, pH,
and turbidity (sediment levels). Growers need to be aware of high levels
of pH (7.5) and high dissolved bicarbonate levels (=\> 5.6 meq/liter).
If water quality analysis indicates these levels, sulfuric acid and/or
gypsum should be injected to acidify the water to lower the pH to
prevent the emitters from clogging with precipitates. A pH of 6.5 is
favorable for injecting fertilizers or other agricultural chemicals into
the system.

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**References:**

NRCS Conservation Practice Standard: Irrigation System, Microirrigation
(code 441)

Water Management: The New Mexico Irrigator's Pocket Guide

Assessing Water Quality Before Installing a Chemical Injection System.
Robert Flynn, Extension Agronomist, NMSU Circular 573, Drip Irrigation
for Row Crops, Aug. 2001.

Maintenance of Microirrigation Systems. Larry Schwanki, Irrigation
Specialist, UC-Davis, NMSU Circular 573, Seasonal or Minimum Tillage,
Drip Irrigation for Row Crops, Aug. 2001.