Planning a drip irrigation system

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When planning a drip irrigation system, there are many factors to consider. The most important of these are covered in this fact sheet.

• water quality
• soil type and variation
• crop variety, rootstock, and likely root zone depth
• number of irrigation shifts and the ability to meet peak daily water requirements
• emitter selection, discharge and spacing
• proposed irrigation management program, such as pulsing or intensive fertigation practices
• surface or sub surface irrigation
• management issues such as frost and heat control
• converting mature plantings

Issues covered in adjoining fact sheets are:

• system maintenance and monitoring
• filtration
• fertigation

Water quality

System blockages are a key issue for drip irrigation. All irrigators, regardless of the irrigation method, should be aware of their irrigation water quality to ensure that it is compatible with the crop and soil. Drip irrigators need to be particularly aware of their water quality as some water sources can create system blockages.

The following water quality issues should be considered when determining if a water source is suitable for drip irrigation:

• pH
• Iron and manganese concentration
• Hardness
• Calcium carbonate saturation index
• Turbidity

For information on how water quality can affect the performance of pressurised irrigation systems, see the Farm Water Quality and Treatment fact sheet on the NSW Department of Primary Industries website. If there is uncertainty about existing water quality, a water analysis should be conducted. A full water analysis will provide a water quality baseline, also help identify the type and level of filtration and possible disinfestation practices needed for the water source.

Matching the system design to the soil and crop type

A soil survey is essential for understanding relevant soil characteristics for irrigation. It classifies soils based on texture and depth, providing valuable information for designing the irrigation system layout.

While the cost of a soil survey is typically small compared to the overall expense of a new drip system, it is a worthwhile investment. It is recommended to hire a soil survey specialist to conduct the survey (Figure 1).

Understanding soil types is crucial for effective system planning. Soil pits reveal soil profiles (Figure 2), providing information on texture, depth, and water-holding capacity. Similar soil types allow similar rooting depths, dripper-wetted patterns, and drainage characteristics providing similar amounts of water to each plant. Wherever possible, the irrigation system should be designed so that similar soil types can be irrigated in the same shift.

A soil survey will also provide ripping, mounding and soil amelioration recommendations. These suggestions are most readily applicable in a new development or redevelopment situation but are also relevant in an existing orchard if drip conversions are proposed. Upgrading to drip irrigation from an existing sprinkler system will not solve inherent soil problems.

Designing the irrigation system according to soil type will help achieve even growth, maturity, yield and fruit quality, allowing efficient irrigation management as each soil type and variety can be irrigated according to its individual requirements. For example, lighter soil types that need more frequent irrigations can be managed independently from heavier soil types where waterlogging is possible.

The results from soil moisture monitoring should reasonably represent the moisture content of each irrigation unit, and a well-designed drip system will help achieve this.

For more information see Soil survey for soil sampling for irrigated horticulture.

Irrigation system design

An irrigation system design is best left to a professional designer who can select the correct equipment to apply the right amount of water at the correct application rate for the soil. Growers should protect their investment by using an Irrigation Australia Limited (IAL) Agricultural Drip Micro Certified Irrigation Designer (CID). A directory of certified designers is available on the Irrigation Australia website.

A correctly designed irrigation system is essential. Experience has shown that systems are more likely to be successful if designed appropriately, installed correctly, and managed well. If any of these aspects are ignored, production potential may not be reached.

Pipeline material, size and class should be the most cost-effective, considering the initial capital cost and the long-term running costs. The design should comply with industry standards such as a maximum emitter discharge variation of ± 5% within a valve unit, and maximum pipe velocity requirements. The pump and motor should be selected for maximum efficiency, considering the size of the planting (current and future), topography and the maximum number of shifts.

The basic components of a drip irrigation system are outlined in Figure 3 below.

When planning a system, look at the quality and suitability of the components rather than choosing them on price alone.

If correctly designed, the drip irrigation system will be able to meet maximum crop water demand. Newly designed systems can usually do this. When expanding a system, especially when using existing pumps, the ability to keep up with crop water requirements may be compromised. Structure the initial design to allow for possible future developments.

Maximum number of irrigation shifts allowed

&#;Irrigation shift&#; refers to the arrangement or aggregation of selected irrigation unit(s) of an irrigation system delivering water at a particular time.

Regardless of the size of the block or the irrigation management program chosen (e.g. pulsing), establishing whether an irrigation system will meet the peak water requirement of a crop can be achieved by determining the maximum number of shifts a system can run. This is a more critical question for drip irrigation than full cover sprinkler systems, due to drip systems having a lower application rate (full cover equivalent), therefore requiring a relatively longer run time to meet crop water requirements. The following equation is used to determine the maximum number of shifts possible for a given drip system and crop type.

Assumptions: Maximum daily water requirement of crop = 8.0 mm/d= 8.0 mm/dSystem application rate = 1.3 mm/h (full cover equivalent)= 1.3 mm/h (full cover equivalent)Daily maximum hours pumping available = 18 h (25% pumping downtime)= 18 h (25% pumping downtime)

In this example, no more than 3 shifts are possible in order to meet peak crop water demand.

Many new drip irrigation developments now adopt low application systems (0.6&#;0.9 mm/hr) over larger areas, with a lower number of shifts (often a single shift).

Using the same daily crop water requirement (8 mm/d) with a low application system (0.9 mm/h), the following is obtained for comparison:

Low flow systems have smaller emitters and therefore require stringent maintenance programs. Visit the Drip maintenance and monitoring page.

More shifts can be run if irrigators are willing to pump 24 hours a day. While this is acceptable, it does not allow any flexibility to cover pump repairs following a breakdown nor allow for extra pumping during heatwaves (where daily water requirements would exceed 8.0 mm/d in the example above).

It&#;s important to ensure that every tree receives the right amount of water. A common issue can occur where plants at the ends of rows don't receive enough water because there are fewer emitters around them. This happens when the in-line drippers are connected to long blank poly offtakes (Figure 4) or when the laterals end too early at the last tree (Figure 5). In orchards running north-south in hot inland regions, the first or last tree on the northern edge often requires more water due to exposure to hot winds. This, combined with a reduced water supply from fewer emitters, can lead to poor tree health.

To ensure these trees receive adequate moisture, ensure that the drip line is run a little closer towards the headland, past the edge of the crop canopy, and use shorter offtakes from the submain and flushing manifold. If the offtakes are too long, another option is to insert button dripper(s) of the same discharge and spacing into the blank offtake (Figure 6).

Choosing an emitter

The emitter &#; or dripper - is the device attached to the drip line or lateral to control the rate of water discharge from the lateral. It is important to choose the right emitter for the irrigation system. Only the more durable (and generally more expensive) drippers and drip lines are suitable for perennial horticulture. Cheaper drip line is normally designed for single season use only, like vegetable crops.

When selecting an emitter, the main properties to consider are:

• Pressure compensating or non-pressure compensating
• Type of dripper, and specialty function, such as non-drain (ND)
• Dripper quality, including manufacturing characteristics and susceptibility to clogging
• Dripper discharge and spacing.

Pressure compensating or non-pressure compensating

Modern emitters can be classified into 2 types: pressure compensating (PC) and non-pressure compensating (non-PC).

PC emitters maintain a consistent discharge within a wide pressure range (between a maximum and minimum). They achieve this by using a flexible membrane or diaphragm that deforms with increasing pressure, restricting the flow path. However, PC emitters cannot increase the discharge if the pressure is too low (e.g., below 5 meters), but they can regulate it at high pressures.

On the other hand, non-PC drippers experience discharge variations with changing operating pressures. In a well-designed and properly operated system, the discharge of non-PC emitters should vary by less than ± 5%.

Hydraulic characteristic of non-pressure compensated drippers

The hydraulic characteristic of an emitter refers to the relationship between the operating pressure and the discharge rate.

In irrigation system design, it is important to ensure that the variation in discharge rate among all emitters stays within an acceptable limit, typically less than ±5% of the design discharge rate.

The hydraulic characteristic helps estimate the maximum allowable pressure variation along the lateral to maintain consistent discharge rates for individual emitters. This minimises the costs associated with piping and pumping while ensuring proper irrigation.

In the case of non-PC emitters, their specified discharge rate (e.g., 2 L/h) is considered the nominal discharge rate at a specific pressure, typically 100 kilopascals (kPa). If the pressure deviates from this specified pressure, the discharge rate of the emitter will also vary (Figure 8).

 Actual discharge rate (L/h)Nominal flow rate (L/h)50 kPa100 kPa150 kPa200 kPa1.30.941.31.561.792.01.432.02.432.793.02.153.03.644.18

Table 1. Pressure and flow rate variation in a common non-pressure-compensating drip system. Source: Adapted from Netafim Australia brochure, Dripline &#; multi-seasonal dripper line.

The emitter discharge exponent (x) describes the relationship between pressure and discharge, indicating the sensitivity of the emitter discharge rate to pressure differences (see Table 2).

The value of x is typically between 0.0 and 1.0. The greater the value, the more sensitive the discharge is to pressure changes. Generally, an emitter discharge exponent of 0.5 or less is acceptable for non-PC emitters used in permanent horticulture. A dripper with a large exponent (for example, x = 0.8) has greater sensitivity to pressure variation than one with a smaller exponent (for example, x = 0.4).

A value of 0.0 means that the discharge rate will not change with pressure. PC drippers have very low x values (in theory 0.0), but generally do show some minor discharge variation in practice.

Table 2 shows that for a 20% change in pressure (due, for example, to friction losses or elevation changes), drippers with x = 0.4 only have a 7.6% change in discharge (see highlighted cells in Table 2). If the same pressure change was to occur for a dripper with x = 0.8, the discharge would change by 15.7%.

The emitter discharge exponent (x) should be available from all drip manufacturers but is rarely available for drip tape or single-season products.

 Emitter discharge exponent (x)0.40.50.60.70.8% pressure change% discharge rate change103.94.85.96.97..69.511.613.615..114.017.120.223..418.322.326.630..622.527.532.838.3

Table 2. The change in percent discharge rate of emitters with various emitter discharge exponents.

Source: Burt and Styles .

Both PC and non-PC drippers use turbulent flow, where water moves through the dripper labyrinth in a very unorganised way due to the internal &#;teeth&#; design of the flow path (Figure 9). Turbulent flow mixes the water, causing it to maintain a high velocity on the dripper wall, sweeping clay and silt particles from the wall into the centre of the pathway and out of the dripper, preventing any build-up or blockages from sedimentation.

Turbulent flow drippers are produced by all major irrigation equipment manufacturers to suit a range of operating conditions (Table 3). All turbulent flow emitters have widely varying performance characteristics and are suited to different applications. Drip irrigation system designers should be aware of these performance characteristics when choosing an emitter for a particular situation to ensure the irrigation system fulfils the basic requirement of uniform water application to the crop.

Types of drippers

Various emitter types are available, and the most common types are outlined here:

DripperDescriptionCommentsOnline drippers

• a barbed inlet port is inserted into the lateral
• drippers are inserted into blank polyethylene pipe after it has been laid in the field (Figure 7)
• emitters are often concentrated around individual trees
• emitters can be either non-pressure compensating or pressure-compensating.

• can produce a restricted root zone concentrated around individual trees
• used in some intensive irrigation/fertigation situations
• can be used to extend the wetted area when inserted into blank offtakes (Figure 6).

In-line drippers

• drippers have emitters inserted or welded inside the drip pipe during manufacture. No external parts protrude.
• Various dripper spacing combinations are available.
• Emitters can be either non-compensating or pressure-compensating.

• no external resulting in less likely damage from pickers or machinery.
• cheaper option than buying individual drippers and inserting them into blank polyethylene.

Non-drain (ND) emitters

• emitters designed so that when a system shuts down, emitters in lower areas do not continue to discharge the water remaining in the lateral and submain.

Suitable in:

• undulating ground (usually 1.4&#;1.5 m only can be held)
• when tightly controlled volumes of water need to be applied, such as during pulsing irrigations. See drip drainage section below

Anti-suck-back (AS) emitters

• emitters are designed to resist vacuuming and prevent sediment from entering back into emitters.

Highly suited to:

• subsurface situations
• surface irrigation on sandy, undulating soils (with the addition of air valves). See Subsurface drip irrigation for perennial horticulture section below.

Anti-root penetration

• emitters are impregnated with a chemical (e.g. copper)

• Chemical impregnation is used to help mitigate (but likely delay) root intrusion in subsurface drip irrigation systems. See Subsurface drip irrigation for perennial horticulture section below.

Table 3. Types of drippers

Dripper quality

The small size of the emitter flow path (typically 0.5-1 mm diameter) requires precise manufacturing. Even small deviations in size can significantly impact the discharge rate.

Ideally, each emitter of the same type would have identical performance and the discharge rate of any emitter along a lateral could be predicted for any given operating pressure.

Tests on various emitter types have shown that most emitters have discharge rates within 2-10% of the average measured rate. However, there have been cases where variations larger than 20% were observed. Such variations would result in inconsistent water volumes, with some trees receiving excessive water while others receive inadequate water.

Coefficient of variation: new drippers are tested by manufacturers to determine how much variability exists in manufacturing. The measure of manufacturing precision is called the coefficient of variation (Cv, see Table 4) and is a measure of the difference in discharge rate of a group of emitters at the same pressure. This measure should also be available from retailers upon request.

ClassificationCvExcellentless than 0.03Average0.03&#;0.07Marginal0.07&#;0.10Poormore than 0.10

Table 4. Emitter coefficient of variation (Cv)

Pressure compensating drippers, due to their relatively complex construction, tend to have a large manufacturing Cv compared to non-pressure compensating emitters.

Another measure that some manufacturers use, particularly for drip tape or single-season products, is emission uniformity (EU%). Emission uniformity incorporates the flow rate variations from both manufacturing (Cv) and pressure variation to estimate irrigation efficiency. The recommended EU is greater than 90%. The calculation of EU is complex and requires knowledge of the emitters Cv. Some manufacturers provide online calculators to determine the EU. Emission uniformity is used by manufacturers for determining the maximum length of a drip line on flat ground given a certain operating pressure and emitter spacing. None of these measurements are interchangeable. An EU of 90%, for example, does not relate to a flow variation of 10%. For more information see Drip system maintenance and monitoring.

Qmin (L/h) = lowest emitter discharge, Qave (L/h) = average emitters discharge, Cv = coefficient of variation, n = number of emitters per plant.

Clogging susceptibility

Two features of drippers that determine how readily they remain clean and functional are the filtration area and labyrinth size (width, depth, and length).

Both features are measurable and should be readily available from dripper specification sheets. Equations are available using turbulence coefficients and effective filtration to provide comparison of dripper clogging susceptibility between products.

Dripper discharge

Dripper discharge should not exceed the soil&#;s infiltration rate. Operating below this infiltration rate will minimise the saturated area immediately under the dripper and avoid run-off.

Traditionally a dripper discharge of 2.5&#;4.0 L/h was considered suitable for lighter soil types, and a discharge of 2 L/h was used in heavier soil types to minimise surface run-off and ponding, promoting deeper water penetration. Today dripper discharges generally lie between 1&#;2 L/h regardless of soil type, combined with a relatively closer dripper spacing.

Dripper spacing

Soil texture also traditionally determined the appropriate dripper spacing. Drippers should be spaced to create a continuous wetted strip along the tree row. In heavier soils, a relatively wider spacing was originally considered sufficient, with closer spacings required in lighter soils to establish this continuous wetted strip.

Closer spacings (0-3-0.5m) are now becoming a common trend in irrigated horticulture, regardless of soil type. This achieves a better wetting pattern in a shorter run time. Some manufacturers can produce drip line with very specific emitter spacings (eg 0.48m) upon request.

Dripper discharge, spacing and soil type

Soil type should still be a factor when determining dripper discharge and spacing. Discharge and spacing affect the wetting pattern in the soil and determine the application rate, which influences how fast water moves into the soil.

Drip irrigation is based on a network of drippers that should distribute water and fertiliser in a uniform pattern to each tree. Although the system can deliver water uniformly, the soil profile might not be wet uniformly.

Immediately under each dripper the soil is saturated, with little air available for plant roots. Correct selection of discharge and spacing can minimise these saturation areas.

Between the saturated zone and the wetting front there is a zone of balanced water and air content (Figure 10). This is suitable for plant uptake of water and nutrients and the volume of this area should be maximised for optimum plant performance.

To use drip irrigation efficiently, a continuous wetted strip along the tree row must be created.

The wetted strip may not be visible on the soil surface between drippers, but it should be around 30 cm below the surface Here the trees can develop a dense root system along the row, using the maximum wetted area that can be made available by the laterals. Saline fronts between emitters along the row are eliminated and the root system will be larger, more efficient, and less vulnerable to water and nutrient stress, generally resulting in healthier trees (see Figure 11).

Soil type dictates the wetted pattern underneath each dripper. In general, sandy soils have large pores which allow water to move freely downward due to gravity. There are only a few smaller pores, and this limits the sideways spread from capillary action. In sandy soils, the wetted patterns tend to be long and narrow.

Heavier clay soils have numerous small soil pores and few larger ones, meaning the water tends to spread sideways and cannot move down freely. In these soils, the patterns produced tend to be shallower and wider for the same volume of water applied (see Figure 12).

However, this generalisation is not true when heavy soils have dried out to such a level that cracks develop in the soil. Once cracks develop, wetted patterns in clays initially tend to be long and narrow, similar to that produced in sands.

The length of irrigation and dripper discharge also determines the size and shape of wetted patterns. A longer irrigation produces a wider wetted pattern for a given dripper discharge and soil type. High discharge drippers produce a wider zone of saturation under the emitter, assisting lateral movement and resulting in a wider wetted pattern for a given irrigation time and soil type.

Pulsing is a drip irrigation management practice which many growers use. Pulsing involves setting up the irrigation controller to turn an irrigation shift on and off (say one hour on, one hour off) throughout an irrigation period. The most commonly claimed benefit is that it encourages greater lateral water movement. A non-drain drip line is ideal for this situation (See drip drainage section below).

Drip application rate

Application rate is the term used to describe the rate at which water is applied to the soil. It is usually measured in millimetres of water applied per hour (mm/h). It relates to a volume of water applied to a given area, and in drippers it is determined by dividing the volume of water discharged from a single dripper into the area that the dripper covers (the product of their spacing).

Assumptions:

Oxygation

All irrigated crops can be exposed to saturated soil under certain conditions. This is especially the case for crops which are drip irrigated as water is delivered to the soil from a point source creating sustained wetting fronts, particularly in heavy soils of low permeability. This scenario has been termed the &#;irrigation paradox&#;; where irrigation is applied to meet the plant&#;s water requirements but at the same time purges air and therefore oxygen out of the rootzone, potentially affecting root activity.

Alleviating this low oxygen environment can be attempted with the use of aerated water for irrigation, increasing oxygen availability in the rootzone. Oxygation is the term used for aerated irrigation water applied through drip irrigation and has been shown to benefit the growth of several crops, particularly in heavier soils.

Oxygen can be added to the irrigation water through a range of methods, including installing simple venturi systems, where the amount of air ingress will depend on the pressure differential across the venturi, or more complex systems such as nano-bubble generators and oxygen injection. Low-rate continuous injection of hydrogen peroxide has also been used to provide oxygen to rootzones.

The most likely scenario when this practice could be considered is with SDI. The benefit is less effective with surface drip irrigation, and ineffective when drip line is suspended above the ground.

Drip line location

Vine crops have one drip line along the vine row, while mature orchards typically have 2 drip lines along the tree row on both sides of the tree. If a third drip line is introduced between these laterals along the butt line (or if the outside laterals are located too close to the butt), care must be taken to avoid problems such as root rot in susceptible crop types.

If developing a drip irrigation system for an orchard, the system should be designed as a 2-drip line system (or 3 as described above), with a single line installed initially to support the young trees (Figure 13).

Trees should be planted directly next to an emitter at spacings consistent with the drip line emitter spacing (such as tree spacings of 1.5 or 2.0 m for emitters spaced at 0.5 m).

This ensures that an emitter is located directly on top of the undeveloped root zone in the first year of planting, supplying adequate water and nutrient to the young tree.

The second line does not initially need to be installed, but if necessary, can be used to grow a mid-row crop to provide some protection from wind or sand damage. Sorghum (Figure 14) or Sudax are commonly grown in these situations. Often a cheaper one or 2-season drip line is used, as it can be difficult to remove the hose from a mature stand of sorghum without damaging the drip line.

In the second year the original drip line used to irrigate the trees is usually moved along the row, moving emitters away from the tree butts to prevent root rot problems. This line only has to be moved half the length of the emitter spacing, i.e. 0.25 m for emitters spaced every 0.5 m.

In the third year the second drip line is installed closer to the trees with each drip line now positioned approximately 0.25 m on either side of the tree. In the following years both drip lines are moved away progressively from the tree line to avoid the trees experiencing dramatic changes to the wetting pattern, while at the same time helping to develop a strong root system to support and anchor the mature tree. The drip lines should finally be positioned 0.5&#;0.75 m on either side of the tree butts, depending on soil type.

For many mature crops it is critical that the drip line does not move significantly throughout the season. Water and fertiliser distribution within the soil, as well as salt movement, should be maintained, allowing a healthy root zone to develop below the drip line. To ensure this occurs, drip lines might need to be staked along the row (Figure 15).

When trees are grown on mounds, a closer drip line spacing is often needed to keep the drip line on top of the mounds. This is generally fine because mounds have well-drained soil that is less prone to waterlogging. Staking the drip lines on each side of the mound near the tree prevents the line from sliding off the mound and keeps it at a safe distance from the tree base to prevent root rot.

Drip irrigation in interplant situations, where there are both young and mature trees, presents challenges. Young trees have small root zones, requiring the drip line to be close to the tree base. Mature trees, on the other hand, need the line to be positioned 0.5-0.75 metres away from the base to avoid root rot issues. One solution is to loop the drip line along the tree line in the early seasons until the young trees have matured. (Figure 16)

Drip drainage

Drip system drainage or drain-out occurs following each irrigation event when the remaining water in submains and laterals continues to run inside the pipework to the lowest point(s) in the orchard and is emitted. Studies have found that emitters in these low areas can emit water continuously between 60-minute irrigation pulses and continue for as long as 24 hours following complete irrigation shutdown.

Drain-out is a concern, especially in large systems with long pipes, frequent irrigation, or pulse irrigation. The more frequent the irrigation event, the more frequently drain-out occurs following each system shutdown/turnoff. There is an increasing level of interest in minimising or eliminating drip drainage. New drip irrigation designs should consider drip drainage at the design stage, particularly if pulse irrigation is being considered. Retrofit options also exist. Options to reduce drip drainage include:

• use of non-drain (ND) drip line
• installation of non-return valves in submains running uphill
• installation of sustaining valves in submains running downhill
• non-leakage valve installation in drip lines
• relocation of valves.

For more information see Drip drainage.

Sub-surface drip irrigation for permanent horticulture

Intermittent interest in sub-surface drip irrigation (SDI) in permanent plantings exists in Australia. There are advantages and disadvantages of SDI in permanent horticulture.

Advantages of SDI are:

• water is delivered directly to the root zone
• less surface water for weed growth
• reduced evaporation from the soil surface.

Actual water savings are not well established There is some thought that if the drip line is below the surface, the soil surface below the canopy will be more barren, exposed to greater temperatures, and that water demand from trees will increase, offsetting the reduction in water use from surface evaporation.

Interest in SDI is often driven by non-water related issues such as removing the drip line from interfering with harvesting nuts from the orchard floor, or mechanical weed control necessary for organic growers.

Placing the drip line below the surface unfortunately creates a new set of challenges. The main disadvantage is that blockages are difficult to detect and locate. Direct observation of the dripper discharge rate is not possible, and it is difficult to evaluate the system and measure the system uniformity. Accurate water meters are therefore essential with SDI to measure application rates and flag blockages or leaks. Blockages may be very difficult to locate until it is too late, and trees begin to show signs of stress. The use of spatial imagery to identify any drip line blockages or leaks is highly applicable for SDI (See Alternative monitoring methods).

Maintenance programs (flushing and disinfestation) need to be carried out more frequently than for surface drip irrigation. Repairs and maintenance costs should also be factored in if considering SDI. Soil may have to be excavated 30cm deep and 2m long before a suspected leak or blockage is found. Frustration can result once a leak is fixed and the system repressurised, only to find another leak exists a little further along.

Blockages can be due to the standard reasons which exist for surface drip irrigation, with SDI additionally prone to blockages due to root intrusion, root pinching, and soil suck-back. In addition, the temperature of irrigation water may drop a few degrees when moving from above to below ground. If dissolved elements such as calcium exist in the water this can precipitate, creating mass blockages in the drip line (See water quality section above).

Root intrusion

SDI systems potentially have the serious problem of root intrusion, particularly when the surrounding soil is dry and crops are looking to scavenge any available water. If herbicide injection to control root intrusion is required, a permit or label extension may be necessary depending on specific regulations.

Modern drip lines are available with chemical (copper) impregnated into the dripper to inhibit root intrusion. It is generally accepted that this may postpone or delay root intrusion, but not completely eliminate it. Root intrusion can also be controlled with acid injection, depending on how severe the intrusion has become.

Even if root penetration is avoided, there is no known method of avoiding drip line pinching, which can occur in vigorous root systems.

Vacuum in laterals

When irrigation ceases in SDI, and the system is shut down, drainage continues in the laterals and sub-main. This can cause a vacuum effect in the laterals, resulting in soil particles being sucked into the dripper orifices, causing blockages. To avoid this, air inlet vacuum relief valves must be installed at the end of each sub-main and flushing manifold, as well as at the high points of the laterals. Non-suck-back drip line products are recommended in SDI situations (see Types of drippers section above).

Insects and rodents

Other problems have been encountered with various insects biting small holes in the laterals, causing seepage, and mice chewing holes in search of water. Standard measures should be used to control these pests. Damage often becomes a particular problem if the system has laid dormant for any length of time (over 6,500 holes reported due to marsupial mice in an installation that lay unused for 2 years due to drought). New drip products claim to deter insect damage by having insecticide embedded directly into the drip line.

Installation

Installing the drip line will require a tine that can carry the drip line into the soil. Depending on the soil type and tractor power, the depth of the lateral can vary. Installation depth should realistically be no more than 30 cm, although limited recommendations are available for permanent horticulture. Some users prefer the drip line as close to the surface as possible. These irrigators are primarily installing the drip line below the surface to avoid damage from machinery such as slashers, and water reaching the surface is not of concern. Installation depth will be a compromise between supplying sufficient moisture to feeder roots near the surface and avoiding excessive water coming to the surface (channelling).

In young orchards, drip line is generally left on the surface for a few years, close to the butt, to enable water to reach the immature rootzone. The drip line can be installed in the correct sub-surface location required for mature plantings once the trees are established (3&#;4 years old). Installation in large mature plantings is difficult as the larger tree canopy (unless heavily pruned) does not allow the installation equipment to install drip lines at ideal distances from the butt of the tree (see Drip line location section above). Damage to rootzones can also be a concern. Therefore, SDI installation in mature trees must be carefully considered.

Several brands of drip line have been used in trials and most reputable brands have proven to be reasonably successful for SDI. AS emitters are necessary, while ND emitters should be avoided. Installing emitters facing up improves lateral water spread.

While SDI is potentially the most efficient system available, growers need to weigh up the disadvantages of such a system before adoption. With continual improvements in management and technology, SDI could become a more favourable option in the future.

Frost control and drip irrigation

Lack of frost control is often viewed as a major disadvantage of drip irrigation. Growers in frost-prone areas have historically preferred using low-level or overhead sprinkler irrigation. If converting to drip irrigation from overhead sprinklers in this situation, seriously consider retaining the overhead system, at least in likely frost pockets.

Low-output frost protection heads can be an option in some instances where drip irrigation already exists. These sprinklers generally operate between 150 to 200 kPa: a pressure that is compatible with most drip systems. The sprinklers are usually mounted on risers above the canopy (Figure 17). Some models (such as flippers) apply water along the tree row only. In these situations, mid-row areas remain relatively dry, meaning these sprinklers can be used to control many more frosts than conventional overhead sprinklers, which can result in waterlogging. These sprinklers also enable a larger area to be frost-protected for a given flow or sub-main size compared with conventional sprinkler systems.

Given the value of water and other issues, frost fans are increasingly being adopted to overcome frost issues in perennial horticulture.

Heat control and drip irrigation

Growers of heat-sensitive crops have also historically been hesitant to adopt drip irrigation, preferring full-cover sprinkler systems (above or below canopy). Purpose built cooling systems, mostly above the canopy (Figure 18), are increasingly being adopted along with drip irrigation in heat sensitive crops. A dual system therefore exists. The cooling system is designed to operate at a similar pressure and flow rate to drip irrigation and is compatible with a drip irrigation design. Cooling systems are operated to reduce temperatures and or increase humidity when conditions require, potentially avoiding damage to crops. These systems have also been used successfully for frost control.

Converting existing plants to drip irrigation

Irrigators are often cautious when converting mature trees or vines from a full cover irrigation method to drip irrigation. Some crop types (and rootstocks) are more sensitive to this conversion than others. Where an established orchard or vineyard is converted to drip, poor crop health and reduced productivity can occur in the first year after conversion if appropriate management practices are not adopted.

Poor tree health, most commonly observed in older trees or trees growing on shallow soil, is often due to a poor understanding of the different management practices the new drip system requires. The most common issue is that irrigators new to drip irrigation often do not initially recognise that more frequent irrigations are required.

The key aim when converting existing trees from full cover to drip irrigation is to quickly encourage enough root growth in the soil volume wetted by the drippers to support the plant during periods of peak water demand.

In some regions salt could have also built up under the tree, where the drippers and soon to be active rootzone are now located. This is particularly the case with furrow and overhead systems, and in un-skirted below canopy sprinkler situations. This salinity needs to be leached quickly. As drip applies water to a relatively small area compared with full-cover systems, the leaching power of drip systems is considerable.

To leach salts away from the tree row, the first few irrigations with drip should be reasonably heavy, considering crop water requirements, water tables and problem areas. Subsequent irrigations need to be scheduled to ensure under-watering does not occur. If the previously existing full-cover system is retained, be aware that frequently using this system could re-mobilise soil salinity back into the dripper-wetted profile.

An ample water supply is usually recommended in the first year after conversion. Growers should not be too concerned about slightly over-watering in the first year. A healthy orchard that successfully overcomes the conversion to drip irrigation can be efficiently drip-irrigated for many years. Applying ample water in this first season also encourages a greater lateral spread of water, which helps minimise the significant change in the new wetting pattern produced when drip irrigation is installed.

To encourage root growth within the wetted strip, it is important to apply soluble fertiliser through the irrigation system (that is, fertigate) early in the season. Use fertiliser high in phosphorus and nitrogen, as this will encourage the development of roots within the wetted strip. Ample phosphorus might exist in the mid-row area, but under drip irrigation, much of this becomes unavailable to the tree. Side banding fertiliser along the proposed drip line location in the season before conversion might also be an option.

When applying fertiliser, time the application over the whole irrigation period, allowing time to flush it from the irrigation system. It is generally recommended to apply nitrogen and phosphorus fertilisers weekly throughout the first season of conversion.

A nematode test and a compaction assessment are also recommended for sensitive crop types. If existing root systems are unhealthy due to nematodes, root rot or compaction, conversion to drip irrigation alone will not correct these problems.

The best time to convert to drip irrigation is normally straight after harvest, as this gives the plant extra time to adapt to the new system without a crop to support. Successful conversions have occurred during less-than-ideal periods, with trees carrying heavy crop loads, but in these situations, the risk of problems occurring is much higher, particularly due to early heatwaves.

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During the first season, no stress should be observed as long as:

• ample irrigation is supplied to maximise lateral spread and leach accumulated salts
• a good fertigation program is adopted.

When converting to drip from an existing pressurised system, the tendency is to use existing pipework where possible. Discuss this with the irrigation designer. Often the effort needed to continue to use this pipework is not worth the small saving in capital cost. Existing asbestos cement submains are unsuitable for drip conversions because they tend to flake, and block emitters when disturbed during installation and once fertigation or injection processes begin. Retaining asbestos cement mainlines can be more acceptable if back-up filters are installed at all valves and, if acid injection is practiced, the pH of the water is kept above 4.5.

Silt and clay build-up in the existing pipework can also render a new drip system ineffective by creating emitter blockages. If this is likely, it is again important to install back-up filters at each irrigation valve (see Filtration for drip irrigation) and to fully flush the system following installation.

It is highly recommended that soil moisture monitoring be adopted at the same time as the new drip system. This will readily identify the irrigation management program required under the new system. Good soil moisture must be maintained in these smaller wetted volumes created by drip irrigation. See the Converting mature citrus from full cover to drip irrigation fact sheet on the NSW Department of Primary Industries website.

Further information

Contact Jeremy Giddings:

Acknowledgements

• Peter Henry, Agronomist, Netafim Australia
• Trevor Sluggett, Agronomy Manager, Nutrien Water, Renmark SA

Bulletin 882

View PDF picture_as_pdf

Previously prepared by Kerry Harrison, Extension Engineer
Revised by Wesley M. Porter and Calvin Perry, Extension Irrigation Specialists

The majority of agricultural irrigation systems in Georgia fit into one of two broad categories: sprinkler irrigation and micro-irrigation. Sprinkler irrigation systems include center pivot, linear move, traveling gun, permanent set, and solid set. Micro-irrigation systems include drip (or trickle) irrigation and micro-sprinklers.

No one system is a best fit for every application. Once you decide to install an irrigation system, you must consider several important factors before deciding which system is best for your situation. These factors include:

• crop
• fuel cost and availability
• initial cost
• labor requirements
• size and shape of field
• water source and availability

In some situations, there may be additional considerations such as whether you own the land or are leasing. You may also own some equipment, such as a well or pumping unit, and wish to adapt the system to this existing equipment. This publication is intended primarily for the farmer who has made the decision to irrigate and is in the process of deciding what type system will best fit into his or her operation.

Center Pivot Irrigation Systems

The center pivot is the most widely used irrigation system on Georgia farms. It is a self-propelled system that rotates around a central pivot point. The drive mechanism for this system may be water pressure, hydraulic oil, or electric motors. Most systems in use today have electric drive systems. The time required for a rotation depends on the system size, pump, or well capacity and the amount of water to be applied at each application; this time can range from hours to days.

The depth of water applied (expressed in acre-inches) in a given application is determined by the speed at which the system moves around the field and the system flow rate. This travel speed is set by the operator and is determined by the desired depth of water to be applied to the field. Since the flow rate to the system remains constant, the more acre-inches of water applied, the longer it will take the system to complete a rotation.

Since center pivots cover a circular area, they are best adapted to fields that are round or square. Because the majority of fields in Georgia are neither, some part of the field may remain unirrigated. On some irregular-shaped fields, farmers may install part-circle systems to as much area with irrigation as possible. These systems generally cost more on a per-acre basis since they are not capable of completing a full circle.

Pipelines on center-pivot systems are generally 5 to 8 in. in diameter, depending on the system capacity and overall system length. Tower spacing (support structure with drive wheels) will vary from 100 to 200 ft. An overhang may be used to extend the coverage beyond the last tower.

Many center pivots have end guns that are large-volume sprinklers located at the outer end of the system. These can be turned on and off as the system moves around the field; they allow the system to water an additional 100 to 150 ft in corners and other irregular parts of the field. Most manufacturers also offer a corner pivot option that consist of an extra span at the end of the system that can swing out and water an additional 300 to 400 ft in the corners of the field. To determine the number of acres covered by a center pivot, use the following formula:

Acres Irrigated = (3.14 x R x R) ÷ 43,560

Where:
R = wetted radius in feet including end gun

Example:
System Length = 900 ft

End Gun wetted distance = 100 ft

Wetted Radius (R) = 900 + 100 = 1,000 ft

Acres Irrigated = (3.14 x x ) ÷ 43,560

= 72 acres (assumes end gun is on 100% of time)

On some systems, provisions can be made to rotate the drive wheels 90 degrees to facilitate moving the machine from one pivot point to another (towable center pivot). Towable center pivots have proven useful for small irregular-shaped fields. They are most common on small adjoining fields (usually 75 acres or fewer). The major advantage of this type of system is that it can be used on more than one field, reducing the initial investment per acre. A major disadvantage is the labor required to move the system.

In the initial design of a center pivot system it is important that the system be capable of supplying the peak water requirements of the crop. For instance, in Georgia, UGA Extension estimates that corn (maize) maximum water use will be approximately 0.34 in. per day, or 2.38 in. per week. A system designed using this criterion will be sufficient to supply the water needs of most any crop grown in this area. To avoid exceeding soil intake rate, a farmer will often divide the weekly amount over two or three irrigation events. For corn, the 2.38 in. divided over three events would mean the center pivot should be designed to deliver 0.79 in. during each event. The required flow rate for a center pivot can be calculated using the following formula:

Q = (453 x A x D) ÷ (F x H)

Where:
Q = required system flow rate (gallons per minute or gpm)

A = total area irrigated by system (acres)

D = depth of water applied per irrigation (inches)

F = irrigation frequency (days per week)

H = hours of operation per day (hours)

Example:
You want a 72-acre system to apply 0.79 in. over 2 days, operating 20 hr per day (40 hr total).

Q = (453 x 72 x 0.79) ÷ (2 x 20) = 643 gpm

Sprinkler Options for Center Pivots

A large number of sprinkler package options are available for center pivots. You may receive conflicting information as to which option best fits your situation, and the choices can be confusing.

The purpose of a sprinkler is to take water from the source (such as the pivot mainline) and distribute the water uniformly over an area in droplet form. In order to cover a large area, a sprinkler must throw water a considerable distance. This requires pressure that translates into fuel consumption at the pump. A reduction in required sprinkler pressure reduces the energy (horsepower) requirements of the pumping system.

As pressure decreases, the area covered also decreases. Thus, as the pivot passes a certain point in the field, if the wetted radius of the sprinklers is decreased, then the intensity of water application must increase to apply a given amount of water. If the application rate exceeds the intake capacity of the soil (infiltration rate), runoff will occur, possibly causing erosion.

Sprinkler packages are available with a variety of operating pressures ranging from 1 pound per square inch (psi) to 100 psi. The lower pressure systems require less energy to operate, but you must ensure that you do not exceed the intake capacity of your soil or, if you do, that you incorporate certain cultural practices to prevent runoff.

Low Pressure Sprinklers

Figure 1. Center pivot irrigation system with low pressure spray nozzles.

Center pivot irrigation system with low pressure spray nozzles.

Figure 2. 360-degree spray nozzles with pressure regulators.

360-degree spray nozzles with pressure regulators.

Low pressure sprinklers usually operate at pressures between 10 and 30 psi. Most of these fall into a category commonly known as spray nozzles that deliver water in a fixed 360-degree spray pattern. They can be installed upright on the top of the pivot pipeline or inverted on drop pipes or hoses below the pipeline. Since they operate at low pressure, the energy requirement is less for this sprinkler compared to most others. These sprinklers have a relatively small wetted radius that results in high application rates. Also, these sprinklers produce larger water droplets that, when combined with drop hoses, reduce losses to wind drift and evaporation.

Use these sprinkler packages only on fields that are relatively flat (slopes less than 5 percent) and have coarse soils (sand, sandy loam, loamy sand) with relatively high infiltration rates.

Low Energy Precision Application (LEPA)

A special type of low pressure sprinkler package available for center pivot systems is called Low Energy Precision Application or LEPA. LEPA systems use ultra-low pressure sprinklers or socks installed on closely spaced drop pipes to apply the water directly on the ground or slightly above the ground surface. The water is often discharged directly in the furrow, so taller growing crops, such as corn, are typically planted in a circular pattern to accommodate the drop pipes.

This system was developed in the Southern Plains of Texas, and its principal advantages include low energy requirements, low wind drift, and low evaporation rates. Avoiding wind drift and minimizing evaporation are primary concerns in the Plains states, where wind velocities are often high and relative humidity low.

The major disadvantage of this system is the extremely high application rates, which will cause erosion on most Georgia soils unless certain practices are implemented. The most common means of overcoming this concern involves furrow-diking and planting in circles, which is done with a specialized implement that creates a furrow in each row middle and constructs a small dike or dam every few feet. These dikes hold the water in the furrow until it has a chance to infiltrate into the soil. Planting in circles has its own set of management concerns for each operator.

Medium Pressure Sprinklers

Figure 3. Center pivot irrigation system with medium pressure impact sprinklers

Center pivot irrigation system with medium pressure impact sprinklers

Medium pressure sprinklers operate at pressures between 30 and 60 psi. They have the advantage of energy savings over higher pressure systems and lower applications rates than low pressure systems. Many of these packages use low angle impact sprinklers, though some manufacturers have other types of sprinklers that fall into this category. These sprinklers are being used widely on fields that are not suited to low pressure systems.

High Pressure Sprinklers

Figure 4. Center pivot irrigation system with high pressure impact sprinklers and end gun.

Center pivot irrigation system with high pressure impact sprinklers and end gun.

High pressure sprinklers operate at pressures greater than 60 psi. They require the greatest amount of energy to operate and offer the lowest application rates. High pressure sprinklers were the only type offered on early pivot systems. Today, their use is limited to fields with fine textured soils, fields with slopes exceeding 10&#;15 percent, and systems that apply wastewater.

Wastewater from livestock lagoons and municipal treatment plants often contain solids that could clog the nozzles on lower pressure systems. Some pivot systems that are required to deliver wastewater with high solids content have been equipped with extra large sprinklers (big guns) with nozzles between 0.5 and 1.5 in. These sprinklers generally require between 60 and 100 psi to operate properly.

Linear Move Irrigation Systems

Figure 5. Ditch-fed linear move irrigation system.

Ditch-fed linear move irrigation system.

Figure 6. Hose-fed linear move irrigation system.

Hose-fed linear move irrigation system.

Linear move systems are similar in construction to center pivot systems except that, rather than rotating around a fixed end point, the entire system moves laterally across the field. They are designed primarily for use on rectangular shaped fields. In general, for a linear move system to be feasible, the ratio of length to width should be at least 2:1; that is, the irrigation system is no more than one-half as long as the lateral travel distance. The system is best suited to fields with a minimum amount of slope (0&#;4 percent).

Most systems are supplied with water from a ditch that extends the length of the field or from a large hose that the system drags along as it travels through the field. Ditch-fed systems will have a pumping unit to pump water from the ditch that is carried by the system. The hose-fed systems are supplied from risers on a pressurized mainline. Either type system can be center fed or supplied from one end. The power for these systems usually is supplied from a diesel-powered electric generator carried on the main control tower, while other systems are powered by a larger electrical cord that is pulled along with the drag hose.

Linear move systems must have a guidance mechanism that guides them in a straight line down the field. Some systems follow an above-ground cable, some follow a buried cable via radio signals, some are designed to follow a furrow the farmer constructs for that purpose, and some now use GPS to provide guidance.

Like center pivots, pipelines on linear systems are generally 5 to 8 in. in diameter, depending on the system capacity and lateral length. Tower spacing will vary from 100 to 200 ft. An overhang may be used to extend the coverage beyond the last tower, and an end-gun may be used on one or both ends. Some farmers choose not to use an end gun due to the fact that they usually do not apply the water uniformly. Sprinkler package options for linear move systems are basically the same as for center pivots.

The linear move system has limited application in much of the Southeast; but in the Coastal Plains, where natural slope is minimal and fields are relatively large, they may be comparable in cost to the center pivot system. Their main advantage is on rectangular shaped fields where a pivot system would leave large areas unirrigated in the corners of the field. These systems generally do, however, require more maintenance than a center pivot because of the more sophisticated guidance system. They also require more labor to operate. This is especially true of the hose-fed systems.

Traveling Gun Systems

Traveling gun systems consist of a large sprinkler (big gun) mounted on a wheeled cart that is mechanically moved across the field, spraying water. The big guns typically discharge between 100 and 600 gpm and will irrigate a radius of from 80 to 250 ft. There are two types of traveling gun systems: cable-tow travelers and hose-pull (or hose-reel) travelers.

Cable-Tow Traveler Irrigation System

Figure 7. Cable-tow traveler irrigation system.

Cable-tow traveler irrigation system.

A cable-tow traveler consists of a large sprinkler mounted on a gun cart and a large, flexible hose &#; one end of which is attached to the gun cart and the other end to a pipe supplying water from the water source. The machine propels itself through the field by winding a steel cable around a drum or pulley mounted on the gun cart. Power to propel the cable winch may be supplied by a water motor, water piston, water turbine, or auxiliary engine. The depth of water application is varied by changing the speed of the cable winch.

Hose sizes are available in diameters from 2.5 to 6 in. Typical lengths available range from 330 to 1,320 ft. The maximum length of run is twice the length of the hose, assuming the hose is connected to the supply pipe in the center of the travel lane. The cable-tow hose is flat when not in use and is stored by winding it on a hose reel.

The cable used to propel the machine is a multi-strand, high strength aircraft type. It must be attached to an immovable object at the edge of the field. A tractor can be used for this purpose, or you can install a "dead man" at the end of each travel lane.

The cable-tow traveler is a versatile machine and can be used on a variety of crops and field sizes and slopes. For most crops (except low growing crops like peanuts), an alleyway is required for the machine. This alley or travel lane may be as little as 6 ft wide for smaller machines or as much as 16 ft wide for larger machines. Clear the travel lane of rocks and other abrasive materials that could damage the hose. Typical travel lane spacings are given in Table 1.

Table 1. Some Performance Characteristics for Cable-Tow Traveler Irrigation System Hose Size Max Travel Distance Maximum Capacity Sprinkler Pressure Typical Lane Spacing Area Covered Per Pass Maximum Hose Pull Range Diam. (in.) x Length (ft) (ft) (gpm) (acres) (psi) (ft) (acres) (lb) 2.5 330 660 165 33 60-70 180 2.1 650-1,000 2.5 500 1,000 165 33 60-70 180 4.1 1,000-1,400 2.5 660 1,320 165 33 60-70 180 5.5 1,300-1,900 3 330 660 250 50 70-80 210 3.2 1,000-1,500 3 660 1,320 250 50 70-80 210 6.4 2,000-3,000 3.5 660 1,320 375 75 80-90 240 7.3 3,000-4,000 4 660 1,320 535 107 90-100 300 9.1 3,500-5,000 4 1,320 264 535 107 90-100 300 18.2 7,000-10,000 4.5 660 1,320 730 145 90-100 300 9.1 4,000-6,000 4.5 990 1,980 730 145 90-100 300 13.6 6,000-9,000 4.5 1,320 2,640 730 145 90-100 300 18.2 8,000-12,000 5 660 1,320 960 192 100-120 330 10 5,000-7,000

Hose-Pull Traveler Irrigation System

Figure 8. Hose-pull traveler irrigation system.

Hose-pull traveler irrigation system.

The hose-pull traveler has four main components: a large reel mounted on a two- or four-wheel cart, a gun cart, a large volume gun-type sprinkler mounted on the gun cart, and a large semi-rigid polyethylene hose. The trailer mounted hose reel is parked at the end or in the middle of a travel lane. Water is fed through the hose to the sprinkler cart. The sprinkler cart is pulled along by the hose as the hose is wound onto the trailer-mounted hose reel. The hose reel is driven by a turbine, water bellows, water piston, or auxiliary engine.

Hose sizes available range from 2- to 5-in. inside diameter. The length varies from 600 to 1,250 ft. These units use a large reel to wind the hose and therefore have a high profile, with some of the larger machines being as much as 12 ft high. This height tends to make the unit top heavy. Always be careful when transporting the machines to prevent them from tipping over.

Design and operation is similar to the cable-tow traveler. The following comparisons can be made between the cable-tow traveler and the hose-pull traveler:

• The hose-pull traveler can be moved in a shorter length of time because there is no hose to reel in and no cable to unwind.
• The hose-pull traveler will require slightly more pressure to operate at the same gpm and hose length because the friction loss through the hose and drive mechanism is usually greater.
• The hose-pull traveler is usually more expensive, but it may be capable of irrigating more acreage because less time is required to reposition it.
• Only the amount of hose that is needed must be wound off the hose-pull traveler, whereas all the hose of the cable-tow machine must be wound off the reel and stretched out so water can flow through the hose. This makes the hose-pull machine easier to use on short runs.
• The hose-pull traveler does not require a separate anchor such as a tractor or earth anchor to which the cable is attached.
• The hose on the hose-pull machine is pulled in a relatively straight line. On the cable-tow machine, the hose is pulled in a loop. In areas with obstructions, this could cause more hose damage on the cable-tow machine.
• A travel lane is not required for the hose of the hose-pull machine. Except in low-growing crops, a travel lane is required for the cable-tow machine.

Both systems use a large sprinkler that requires a relatively high operating pressure&#;80 psi at the gun. Since pressure is lost traveling through the hose, mainline, and drive mechanism, the pump operating pressure is usually high&#;as high as 150 psi on a typical 550 gpm machine. This requires more horsepower and thus more energy consumption than a comparable center pivot system. Also, labor requirements for traveling gun systems are considerably higher than for a center pivot system.

Table 2 gives the inches of water applied by traveling gun sprinkler systems based on sprinkler output, lane spacing, and travel speed. Note: As of the most recent revision, it appears there are no current manufacturers of cable-tow irrigation systems. There continue to be several manufacturers of hose-pull (hose-reel) systems in operation.

Table 2. Inches of Water Applied by Traveling Sprinklers GPM Lane
Spacing (ft) Travel Speed, Inches/Minutes 6 12 18 24 36 48 60 72 96 120 50 105 1.5 0.8 0.5 0.4 &#; &#; &#; &#; &#; &#;   155 1 0.5 0.3 0.3 &#; &#; &#; &#; &#; &#; 100 130 2.5 1.2 0.8 0.6 &#; &#; &#; &#; &#; &#;   190 1.7 0.8 0.6 0.4 &#; &#; &#; &#; &#; &#; 150 145 3.3 1.7 1.1 0.8 0.6 0.4 0.3 &#; &#; &#;   215 2.2 1.1 0.7 0.6 0.4 0.3 0.2 &#; &#; &#; 200 160 &#; 2 1.3 1 0.7 0.5 0.4 &#; &#; &#;   235 &#; 1.4 0.9 0.7 0.5 0.3 0.3 &#; &#; &#; 250 175 &#; 2.3 1.5 1.1 0.8 0.6 0.5 &#; &#; &#;   260 &#; 1.5 1 0.8 0.5 0.4 0.3 &#; &#; &#; 300 180 &#; 2.7 1.8 1.3 0.9 0.7 0.5 0.45 &#; &#;   265 &#; 1.8 1.2 0.9 0.6 0.5 0.4 0.3 &#; &#; 400 200 &#; 3.2 2.1 1.6 1.1 0.8 0.6 0.5 0.4 &#;   300 &#; 2.1 1.4 1.1 0.7 0.5 0.4 0.35 0.27 &#; 500 225 &#; 3.6 2.4 1.8 1.2 0.9 0.7 0.6 0.45 0.3   330 &#; 2.4 1.6 1.2 0.8 0.6 0.5 0.4 0.3 0.2 600 240 &#; &#; 2.7 2 1.3 1 0.8 0.67 0.5 0.4   365 &#; &#; 1.8 1.3 0.9 0.7 0.5 0.44 0.33 0.26 700 250 &#; &#; 3 2.2 1.5 1.1 0.9 0.75 0.56 0.45   375 &#; &#; 2 1.5 1 0.8 0.6 0.5 0.37 0.3 800 260 &#; &#; 3.3 2.5 1.6 1.2 1 0.82 0.62 0.5   385 &#; &#; 2.2 1.7 1.1 0.8 0.7 0.56 0.42 0.33 900 300 &#; &#; &#; 2.4 1.6 1.2 0.96 0.8 0.6 0.5   360 &#; &#; &#; 2 1.3 1 0.8 0.7 0.5 0.4 1,000 330 &#; &#; &#; 2.4 1.6 1.2 0.97 0.8 0.6 0.5   400 &#; &#; &#; 2 1.3 1 0.8 0.7 0.5 0.4 Depth of application = 19.26 gpm ÷ (Lane spacing (ft) x Travel speed (in./min))

Solid Set and Permanent Set Irrigation Systems

Figure 9. Permanent set sprinkler irrigation system.

Permanent set sprinkler irrigation system.

Solid set irrigation systems consist of portable, aboveground aluminum pipe with sprinklers spaced at specific intervals along the pipe. Permanent set systems consist of buried pipes (usually PVC plastic) with evenly spaced sprinklers mounted on risers. These systems are typically used on small acreages and/ or crops that have a high cash value such as sod or vegetables. Permanent set systems are also frequently used as under-tree sprinkler systems on pecans and as overhead systems for frost/freeze protection on apples, citrus, peaches, blueberries, and strawberries.

Usually impact sprinklers are used, which can be either single nozzle or double nozzle. Spacing will vary between sprinklers, depending on sprinkler size and nozzle size. Typical spacings are in the 40 to 60 ft range, although large volume, gun-type sprinklers may be spaced as much as 250 ft apart.

Labor requirements for solid set systems can range from low to high, depending on how much pipe is available and how often the sets must be moved. Permanent set systems require very little labor and can easily be automated. Permanent set systems are also one of the most expensive in terms of initial cost per acre.

Micro-Irrigation Systems

There are many variations of micro-irrigation, but they all fall under two general categories: drip (or trickle) irrigation and micro-sprinkler irrigation. In general, micro-irrigation systems distribute water uniformly to a crop via low-volume, low-pressure devices that control the rate of water output. Examples of such devices include drip emitters, drip tape, and micro-sprinklers. Advantages of micro-irrigation over other types include:

• water conservation (uses 1/3 to 1/2 less water compared to other methods because of lower losses from wind and/or evaporation)
• energy efficient
• fewer weed problems since systems do not generally wet the entire ground surface
• area between rows remains drier, facilitating spraying, harvesting, and other cultural operations
• can be used for fertigation
• reduced labor compared to some other methods
• can be easily automated

Drip Irrigation Systems

Figure 10. Components of typical drip irrigation system.

Components of typical drip irrigation system.

Drip irrigation was first used in Georgia in the mid-s primarily on orchard crops such as pecans, peaches, and blueberries. It is currently the most popular method used on these types of permanent crops. It is also widely used in ornamental nurseries, and a different form of drip irrigation is also being used on vegetables and strawberries grown on plastic mulch. In some cases, drip irrigation either has been temporarily (annual basis) or permanently installed into row crop fields to cover areas not covered by other irrigation types. Drip irrigation can be categorized into either "point source" or "line source" type systems.

Figure 11. Examples of point source emitters.

Examples of point source emitters.

Most orchard crops and other permanent type crops use what is commonly referred to as point source emitters. These are output devices that are typically attached to 0.5- inch to 0.75-in. polyethylene supply tubing. Output rates for point source emitters are generally 0.5, 1, or 2 gallons per hour. The number of emitters per plant will vary from one to 16, depending on the type and size of the plant being watered. For example, a mature peach tree might require twelve 2-gallon-per-hour emitters.

These systems are usually designed to operate every day during the growing season when the weather is dry to supply the daily water needs of the crop. Systems are generally designed so any one zone will not operate more than 12 hr per day. This prevents creating a permanent saturated soil condition, which could damage roots.

Point source emitters and supply lines may be installed on the ground surface or buried a few inches beneath the surface. On widely spaced crops such as pecans, the emitter lines are usually buried to prevent physical damage to the system and to facilitate field operations such as spraying and harvesting.

Figure 12. Manifold supplying drip irrigation tape under plastic mulch on bell peppers.

Manifold supplying drip irrigation tape under plastic mulch on bell peppers.

A different type of drip irrigation is being widely used on high cash-value crops such as tomatoes, peppers, and strawberries. This system uses what is sometimes called a line source emitter or drip tape. This product consists of a thin-walled polyethylene tape with discreet outlet points built in. The outlets may be anywhere between 4 and 24 in. apart. Typical outlet spacings for vegetables and strawberries are 9 and 12 in. Water output rates are between 0.2 and 0.5 gallons per minute per 100 ft of tape. With outlets spaced so closely together, the end result is a continuous wet strip that makes this product ideal for watering rows of closely spaced crops. Wall thicknesses for the tape can be anywhere between 4 mils and 20 mils, with 8 to 10 mils being the most common.

When used for growing vegetables or strawberries, drip tape is almost always used with the production practice known as plasticulture. The crops are planted on a raised bed covered with a plastic mulch. Usually the beds are fumigated to control insects, diseases, and weeds. The drip irrigation tape is installed in the center of the bed at the same time that the plastic mulch is laid. The drip tape may be installed on top of the bed directly under the mulch or a couple of inches beneath the soil surface to help prevent rodent damage. The drip irrigation tape is used to supply water underneath the mulch. Most growers also inject fertilizer into the system throughout the growing season to provide nutrients in prescription amounts.

Drip tape is being used widely across Georgia for irrigating blueberries and, to some extent, pecans. On permanent crops such as these, the tape is usually installed 6 to 8 in. deep. Also, since the tape is expected to last several years on these crops, growers generally use thicker-walled tape&#;15 to 20 mils.

Recently, drip tape has been used to irrigate row crops (cotton, corn, peanuts). This application of drip tape is referred to as subsurface drip irrigation (SDI). The tape is usually installed 9 to 15 in. deep in every other middle row, so one tape supplies two crop rows.

All drip irrigation systems require clean water to prevent clogging of the emitters. For this reason, use a filter on any drip system regardless of the water source. On most groundwater wells, a fine-mesh screen or disc-style filter is sufficient unless the well pumps large quantities of sand; then a centrifugal sand separator may also be required. Surface water sources generally require a sand media filter to remove suspended solids, algae, etc. Use the sand filter in conjunction with a screen filter installed downstream.

Many systems, particularly those that use surface water, may experience organic growths of algae or bacteria that will eventually clog emitters. These problems can usually be controlled with periodic injections of chlorine into the system. Periodic injections of acid solution may also be required if you experience a build-up of mineral deposits such as calcium or magnesium.

Micro-Sprinkler Systems

Figure 13. Example of a micro-sprinkler.

Example of a micro-sprinkler.

Micro-sprinkler systems are very similar to drip irrigation systems except that, rather than discharging water at discreet points, the water is sprayed out through a small sprinkler device. These micro-sprinklers are typically made of plastic and are available in a multitude of flow rates and spray patterns.

One advantage of the micro-sprinklers compared to drip irrigation is that they disperse the water over a larger surface area (3 to 10 ft diameter). This is especially advantageous on sandy soils where water applied from a drip emitter tends to move vertically downward, which can cause insufficient root volume being irrigated. For this reason, micro-sprinklers are used extensively in south Florida on citrus crops where sandy soils are prevalent.

Micro-sprinklers may also be advantageous over drip irrigation where water quality is a concern. Because they have larger orifices than drip emitters, micro-sprinklers tend to be less prone to clogging. Since the water is sprayed above ground, a farmer can more easily detect when he has a problem.

Micro-sprinklers have been used to some extent in Georgia on pecans and a few other orchard crops such as peaches. Since they must be installed above ground, they may be more prone to physical damage than other types of drip irrigation systems.

Energy for Irrigation

Most farmers in Georgia use either electricity or diesel engines to supply power for their irrigation systems. A few use propane, natural gas, or gasoline.

Figure 14. Large agricultural well with electric motor.

Large agricultural well with electric motor.

Figure 15. Diesel powered pumping unit on pond.

Diesel powered pumping unit on pond.

Some electric suppliers offer electricity for irrigation purposes at a special rate. Many also require that the power source be interruptible. This means that the power supplier can shut off power for a few hours each day during peak demand periods. Some electricity providers offer time of day pricing with discounts for off-peak usage. This possibility should be considered in the initial design of the system.

If electric power is being considered as a power source, be sure to account for all costs associated with it, such as line extension charges, monthly minimum (standby) charges, and the rate you will pay for actual electricity use. These costs vary from one power supplier to another, and you should discuss these costs with the electric supplier before signing a contract.

An additional consideration is whether or not three-phase power is needed. Depending on where you are located on their distribution system, most power suppliers will limit you to 10 or 15 horsepower on single-phase lines. If more horsepower is required and three-phase power is not available on or near the farm, the cost to construct power lines may be prohibitive.

Many farmers choose electric power whenever possible because of the low maintenance and quiet operation. However, if electric power is not available, or if the cost is prohibitive, diesel powered engines are usually the second choice, especially for systems requiring more than 30 horsepower.

The most important factor in selecting an electric motor or internal combustion engine to supply irrigation water is horsepower (hp). The equation for calculating required horsepower for pumping water is:

HP = (Q x H) ÷ (3,960 x E)

Where:
Q = system flow rate (gpm)

H = total head in feet (multiply psi by 2.31 to convert to feet)

E = operating efficiency of pump (as a decimal)

Example:
A pump must deliver 900 gpm at 300 ft total head. The pump efficiency is 75 percent. What size electric motor is required?

HP = (900 x 300) ÷ (3,960 x .75) = 91 hp (a 100 hp motor would be selected)

Note: Concepts such as total head, pump operating efficiency, etc., are beyond the scope of this publication.

In general, electric motors may be selected to operate at 100 percent of their rated horsepower (they have a built-in overload factor). However, for internal combustion engines, the general practice is to calculate the horsepower required and then add 15 percent to determine the continuous horsepower rating of the engine. This provides a built-in safety factor to prevent overloading the engine, particularly after it begins to experience some wear.

Water Sources for Irrigation

Water sources for irrigation in Georgia include surface water and ground water. Remember that water for irrigation is needed most when water supplies are at their lowest level. Water sources should, therefore, be adequate to supply water during extended dry periods.

Since , all large agricultural water uses in the state require a water use permit from the Environmental Protection Division, Department of Natural Resources (GA EPD). This law applies to any agricultural water use that averages more than 100,000 gallons per day in any one month (3 million gallons in a month). Any water withdrawal that exceeds 70 gallons per minute will generally require a permit. This law applies to both surface water and ground water withdrawals.

Changes in Agricultural Water Use permits are occurring on almost an annual basis. Anyone considering installing a new water withdrawal (surface or ground) point or purchasing property with existing water permits should contact the GA EPD water management office for guidance and assistance. Your county Extension agent can also help.

Since , all large agricultural water uses in the state require a water use permit from the Environmental Protection Division, Department of Natural Resources. This law applies to any agricultural water use that averages more than 100,000 gallons per day in any one month (3 million gallons in a month). Any water withdrawal that exceeds 70 gallons per minute will generally require a permit. This law applies to both surface water and ground water withdrawals.

Surface Water

Surface water is available in two primary forms: ponds and streams (rivers). Use of streams and rivers is limited in Georgia because they are often not located near the farmland. This is especially true in the southern half of the state, where many of the waterways are surrounded by large swamps.

Farm ponds make up a considerable portion of the irrigation water used in the state.

The required size of an irrigation pond is based on the number of acres to be irrigated. For most areas of Georgia, the general rule is 1 acre-foot of water storage for each acre of land to be irrigated. A 10-acre pond with an average depth of 10 ft would be needed to irrigate 100 acres approximately 12 times (0.75 in. per application). This rule assumes no recharge to the pond from ground water or underground springs. If you have a spring-fed pond, adjust the storage capacity of your pond accordingly.

If you have an existing pond that is not adequate to supply all water needs of your irrigation system, you may opt to install a well to pump open discharge into the pond to maintain its water level. The size of the well needed to supplement the pond depends on the storage capacity of the pond and the size of the irrigation system.

Before constructing any new pond, check with appropriate local authorities to determine if permits are required and to ensure that wetlands regulations are not being violated. The USDA Natural Resources Conservation Service often can provide assistance.

Ground Water

The use of ground water for irrigation increased dramatically in Georgia during the s and s. In general, ground water is readily available in the southern half of the state below a line running from Augusta to Columbus. This section of the state is underlain by several aquifer systems consisting of porous materials like limestone, sand, and gravel. Depending on location and depth, wells in this part of the state may yield as much as 3,000 gallons per minute.

The majority of the northern half of the state is underlain by igneous rock such as granite and gneiss. These consolidated rock formations are basically impermeable and water can only be obtained where the well intersects cracks and fissures in the rock that contain water. Typical well yields are from 5 to 10 gallons per minute, which is not adequate for most irrigation systems. Occasionally, a lucky landowner will get a well that yields up to 100 gallons per minute, but this is rare. Most irrigators in north Georgia use surface water as their water source.

Most wells in south Georgia that are 6 in. in diameter or larger will require the owner to obtain a withdrawal permit from the state via GA EPD.

Additional Resources

The UGA C.M. Stripling Irrigation Research Park website has numerous resources available to supplement this publication, such as links to manufacturer websites, other Extension publications, state and federal resources, tutorials, etc. https://striplingpark.caes.uga.edu/resources.html

In addition to the C.M. Stripling website, four irrigation equipment economic enterprise budgets for both electrical and diesel pivots of 65 and 160 acre sizes can be found on the UGA AgEcon Extension budgets and tools website: https://agecon.uga.edu/extension/budgets.html

Anthony W. Tyson, former Extension Engineer, contributed to earlier versions of this publication.

Status and Revision History
Published on Sep 12,
Published on Feb 20,
Published on May 14,
Published with Full Review on Feb 16,
Published with Minor Revisions on Dec 23,
Published with Minor Revisions on Dec 07,

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