1. Flushing of distribution system
The easiest and most cost effective form of maintenance is regular flushing. The frequency of flushing varies from weekly to monthly depending on water quality.

Flushing of Laterals
Again, this should be done more frequently in warmer weather. Ensure when each lateral is being flushed it has a full bore discharge. This will ensure any contaminants present are expelled from the system. The use of flushing manifolds greatly simplifies this procedure.  Balance the frequency of flushing and chlorination with seasonal changes and internal condition of the T-TAPE. Warmer weather usually equates to higher loads of algae, bacteria and carbonates in the system.

Flushing of Fertilisers
Incomplete flushing of fertilisers from laterals can promote root intrusion and will promote growth of algae/bacteria. Flushing of fertilizer is achieved simply by irrigating for one hour after injecting all fertiliser into the system.

CAUTION: ACID SHOULD ALWAYS BE ADDED TO WATER, NEVER ADD WATER TO ACID

In order to obtain good results, the plugging should be only partial. If the system is completely plugged, the injection of acid may be ineffective. Acid is used to clean pipes and emitters of mineral deposits that have accumulated in the system over time.

These minerals may have precipitated naturally from the water or by use of incompatible chemicals or fertilizers. (see the fertilizer compatibility chart). Acid treatment may also be used to improve physical and chemical properties of your soils.

More commonly, acid treatments are used to dissolve deposits such as:

• Iron Oxides
• Calcium or Magnesium Carbonates
• Cleaning Bacterial Slimes

• Fill soil profile with usual irrigation water. This will allow immediate dilution as any acid enters the root zone.
• Calculate accurately the required injection time.
• Shut the system down leaving the acid solution in the line for a minimum of 1 hour, preferably 5 plus hours.
• Flush laterals thoroughly.
• Continue irrigation to further dilute acid if you feel the need, eg 1-2 hours.

Safety Precautions
Acids are dangerous and highly toxic. It is critical to read carefully and follow all instructions.
Ensure that proper protective clothing, breathing apparatus and goggles are worn at all times when handling acids.

Corrosion
Acids are corrosive to iron and some other metal pipes; PVC and polyethylene are resistant to acid.
In order to avoid any damage from acid remaining in the pipes after treatment, maintain a continuous flow of water through the system after treatment to flush the acid solution away from head control systems (filtration and valves), eg 2-5 minutes depending on length of mainline.

Type of Acid Used

Nitric Acid -36°Baumé density 1.33
Hydrochloric Acid 33-35%
Sulphuric Acid 90%
Phosphoric Acid (food grade) 85%
(Do Not use Green Phosphoric Acid – too many impurities)

Concentration and Duration of Treatment
The amount of acid required to reduce your pH to, for example pH 2.5, may differ from your neighbours depending on the type and amount of dissolved salts in the water. Therefore, each water supply should be acid calibrated. Examples of acid calibration are shown in a later section called “Sample Calculations”.
The procedure is as follows assuming the following criteria:

• If it takes 500ml of acid to bring 1000L to a pH of 2.5 (explained in “Sample Calculations”.
• The system uses 60,000L/hr.
• It takes 30 minutes of acid injection to give necessary treatment (explained in “Sample Calculations”).

Then in 30 minutes (½ hour) you need to treat 30,000L (60,000L x ½ hour).
500ml need per 1000L = 500ml x 30
= 15,000ml
or 15 litres of acid.
HOW TO CALCULATE INJECTION TIME is demonstrated in “Sample Calculations”.

3. Chlorination
It is essential, for systems using open water sources, that a chlorination or biocide program is implemented for control of:

• Algae related problems.
• Sedimentation of organic particles.
• Bacteria and bacterial slimes in the system.
• Filtration efficiency.
• Organic sediments in the system.

Systems supplied by bore water still require 2-4 acid treatments per year due to bacterial growths that occur.

Five major points to follow:
1. Prevention is better than cure. Conditions inside the T-Tape do not remain static, so constant monitoring of the drip irrigation hose or assessment of ontaminants while flushing the system is very important.

2. Duration of injection time. Ensure you inject long enough for chlorine to reach the furthest point of the field. Average velocity through the system is 1 metre every 3 seconds or 1 foot per second from the point of injection. For a more accurate assessment, inject food dye into your system and record time taken for coloured water to reach furthermost point of the drip system.

3. Test residual strength. Whilst you might have calculated for say 3ppm of chlorine to be injected you need to know what the residual chlorine level is. As the chlorine travels through the system some is utilised and absorbed, so you may need to increase the dosage rate to counter immediate absorption in the system, aiming for a 1-2ppm residual level.

4. Generally there are three chlorination methods used:

Chlorine’s biocidal activity is best when pH of solution is 6.5 or below.

Source of Chlorine
Chlorine can be sourced in three forms:

1. Liquid Chlorine Sodium Hypochlorite (easy to use).
2. Solid Chlorine Calcium Hypochlorite (easy to use).
3. Gaseous Chlorine – sophisticated equipment required.

To calculate the amount of chlorine required to obtain correct ppm (15ppm) is explained in the Sample Calculations

See T-Tape Fittings

1. Root intrusion
Drip tube emitters with hole outlets are susceptible to root intrusion. T-Tape has been innovative with its slit outlet which dramatically reduces the incidence of root intrusion, simply because the root has more difficulty in finding the outlet.

Root intrusion is a direct function of the plant being stressed due to lack of water. Roots and root hairs have a natural tendency to spread out and search for nutrients and moisture. They are only attracted to the emitter if they are stressed or if nutrient is not flushed from the system. More precisely, an acid treatment of 2-3 pH will assist to clear partially blocked emitters.

Should intrusion take place, it can be dislodged or literally burnt out using nitric, hydrochloric, phosphoric or sulphuric acid. To effectively treat intruding roots, a solution with a pH of 2-3 is required. For more detail refer to section on “Acid and Chlorine Treatment” and their respective sample calculations. Chlorine at 200-500ppm has been found to assist in dislodging roots.

Root intrusion may also occur where the system is operating at low pressures.

Avoid operating the system below 0.56 bar.

For permanent installations using wall thickness of 10mil or greater, it is preferred to operate systems between 0.7 - 1.05 bar. If the root has blocked the emitter to 0% flow, you may never clean the system.
Prevention is always the preferred approach. The use of herbicides is being investigated for the prevention of root intrusion.

In summary, to prevent root intrusion:

• Avoid moisture stress
• Operate system at 0.7 - 1.05 bar
• T-Tape Slit Outlet dramatically reduces the incidence of root intrusion
• Use of trifluralin at the rate of 0.1L/ha is registered for use in sugar cane.

2. Insect damage
The incidence of insect damage (crickets, wire worms, grubs, etc...) is a direct relationship with insecticide control measures.

Some insecticide control measures are used.

The use of plastic mulch creates a micro-environment that increases insect activity, particularly ground crickets.

Symptoms:  Generally no problems on first watering. On second and subsequent waterings, leaks are encountered. Insect activity also seems to be increased after rain.

Solution:  Having had the insect causing the damage identified by an entomologist, follow through on his recommendations. If injecting chemical through the drip system is a recommendation, it is generally a good idea to wet up properly before injecting. The active ingredient of most chemicals often has the tendency to lock up quickly on contact with clay particles, therefore restricting its movement within the root zone. A definite advantage would be obtained by using 20cm emitter spacing. Drip irrigation has been known to increase mobility of certain elements in the soil, eg phosphorous.

It may be best to incorporate chemicals during bed preparation. With some chemicals, if they are left exposed to the sun, their effectiveness can be reduced dramatically.

3. Suckback
Where field layout is on sloping ground, upon shutdown of the system, water will flow to the lowest point.
If air is not allowed to enter the system by means of an air/vacuum release valve, a vacuum will be created in the highest end of the tube. Soil particles can be sucked back into the regulating tube. This will gradually block and cause stress to the plant.

Once again emitters with hole outlets are far more prone to suckback problems than T-Tape with it’s slit outlet.

Upon inspecting a field for low output of water and you suspect suckback, complete the following checks:

• Examine elevation layout of field.
• Ensure that the T-Tape is operating at normal pressures.
• In shallow installations where flow has ceased, rub drip tape between fingers 5 cm either side of emitter.

• Use T-Tape with slit outlet.
• Use an air/vacuum release valve connected to the submain.
• Operate the system at the highest recommended pressure.
• Inject surfactant that may assist in dislodging particles.

A very accurate procedure to ascertain injection time is to inject a dye following the pressurisation of a system. 

Measure time from first injection until the colour solution reaches the furthermost point in the block to be treated. 

If you wish to run an acid solution through each emitter for a minimum of 5 minutes, then simply add 5 minutes to your injection time calculated above.

2. Acid calibration of irrigation water

3. Calculation of acid required to reduce the water to PH2
Duration of injection treatment = 30 minutes.
Conduct a test on a 200L sample of water to lower the pH.
Continue adding small amounts of acid until pH reaches 2.

For this sample calculation let us assume that to lower the pH to 2 requires 120ml of acid per 200L water = 600ml per 1000L (1m3) water. Assume a flow rate of 31,000 L/hour (31m3).

4. Calculation of injection rate of chlorine
Check your flow rate, if possible with a flow meter.

For this example, assume the flow rate is 31,000L/hour which equals 31 m3/hr (cubic meters), the desired rate of chlorine is 15 ppm and the active ingredient of chlorine is 12.5% or 125 ml/L.

5. Calculation of total quantity of chlorine required

6. Achieving desired PPM (parts per millon)
When calculating for chlorine, chemicals and fertilizer concentrations:

The number of growers applying fertilizers through their irrigation systems has risen dramatically over the last few years. With the assistance of plant tissue and sap analysis, growers are now able to “fine tune” their nutritional programs to maximise yields.

When growers are selecting the products to suit their nutrient requirement, factors such as solubility, compatibility and reaction with salts in the irrigation water must be taken into account. Good quality fertilizers limit the risk of plugging.

The amount of fertilizer which can be dissolved depends on the water temperature, the type of fertilizer and whether other products are contained in the solution.

Check the pH of the solution and the conditions of use in order to obtain total solubility. Flush the laterals thoroughly after the injection period.

Table 1: Solubility of the more commonly used fertilizers

Table 2: Difference in solubility with temperature change

The compatibility of these products is important if you intend mixing them. Also remember, less of each product will be able to dissolve if you are using two or more products

Table 3: International Conversions for Concentration of Solutions