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How to select the best fertilizer injecting / dosing system

January 22, 2018

With numerous types of fertigation systems available it can be confusing to select the most appropriate system. This article will step you through the selection process.

[Aside: If you are not familiar with the various types of fertigation systems, please refer to our article here. To assist you work through the selection process, a summary specification sheet of fertigate's fertigation systems is available. For full details, please refer to the detailed manuals and product information contained on our web site for each product.]

The primary design questions and information you require to select an appropriate fertigation system are:

1. Fertilizer Concentration
2. Maximum & Minimum water flow rates
3. Maximum & Minimum water Pressure available upstream of the fertigation system
4. Maximum & Minimum water Pressure required downstream of the fertigation system
5. Fertilizer Dose rate accuracy & ease to set dose rate
6. Intended Fertilizer frequency
7. System versatility / intended use
8. Frequency you will change fertilizers / seaweed extracts
9. How easily and frequently do I want to replenish the fertilizer storage
10. Ease to check available fertilizer level
11. Ability to validate system operation

Items 1 to 4 are the parameters determining the fertigation system “CAPACITY or SIZE”.

Items 5 to 12 allows you to select the “TYPE” of fertigation system appropriate for your needs.

To assist the selection process, print and record your information on the form below.

 How to select the right fertigation system

1. Fertilizer Concentration

Read the label of each type of fertilizer / seaweed extract to be used and record the manufacturers recommended fertilizer concentrations. Different manufacturers use different units (eg “xx” ml of fertilizer / 9L of water or “xx” ml of fertilizer /10L of water, % fertilizer or “xx” fl oz. of fertilizer / USG etc).

To select a suitable fertigation unit, record common fertilizer concentration units. To assist you we included a conversion chart in the “Recording sheet”. Please contact us if you would like further information.

Compare fertilizer concentrations to be used - with the fertigation equipment you are considering.

2. Maximum & Minimum Water Flow Rates

Whilst not immediately apparent, you will use significantly different flow rates performing different tasks eg Hosing paths uses significantly more water than fertilizing your bonsai, orchids or vegetable garden. Your fertigation system does not have to perform all tasks. Use a "twin" tap outlet - one of the path and the other for your fertigation system.

Only consider water volumes you want your fertigation system to deliver. There are several ways to calculate or measure your required water flow, some of which are:

Hand held hose.
Measure the time taken to fill a watering can and calculate the flow rate as follows:
eg 35 seconds to fill a 1 USG watering can equates to:
Similarly, 45 seconds to fill a 10L watering can equates to:
Drip Irrigation
You may want to use your fertigation system with a drip or other form of irrigation system. This is more challenging to measure water flow unless you have an in-built flow meter.
Assuming you do not have a flow meter, note the type and quantity of each drip irrigation device – dripper, sprayer etc
Refer to the manufacturers specification and record the water volume that each dripper or sprayer emits.
Multiply that volume by the number of each device type. Summing these values will provide the volume of water your drip irrigation system uses.

Record the maximum and minimum water flow.

3. Maximum Water Pressure Upstream Of The Fertigation System

It is important that your chosen fertigation system is compatible with the upstream water pressure.

Some fertigation systems require a certain pressure differential between the upstream and downstream pressure to ensure there is sufficient “pressure drop” to enable the system to operate (eg Venturi systems often require a pressure differential of 25% - 30% across the fertigation system).

Use a pressure gauge to measure the upstream water pressure. These gauges are cheap and can be purchased from most hardware or plumbing outlets. Maximum pressure can be recorded when no water is flowing through the system.

Record the maximum UPSTREAM water pressure.

4. Maximum & Minimum Water Pressure Required Downstream Of The Fertigation System

Water pressure downstream of the fertigation system is important.

We spoke above about the 25% - 30% pressure differential typically required for Venturi's to operate. Other fertigation systems include an "in-built" pressure reducer which limits downstream water pressure to say 180kPa or 26 psi.

It is important to know your required downstream pressure to select the appropriate fertigation system.

Three “downstream” pressure situations immediately come to mind:

  • Hand held hoses require negligible pressure (other than to overcome the spray rose and some inherent pressure losses.
  • Some drip irrigation systems MUST operate below 180kPa to ensure they don’t literally “blow” themselves apart.
  • Some irrigation systems incorporate “pop up" type sprinklers which require a high pressure to “pop up” and start irrigating.

You may like to use a pressure gauge to assist you arrive at the various pressures.

Review and analyse the scenarios you intend to use you fertigation system and record the maximum and minimum DOWNSTREAM water pressures required.

5. Fertilizer Dose Rate Accuracy & Ease To Set Dose Rate

Fertilizer dose rate accuracy is important when selecting a fertigation system.

If you simply want to “slosh” fertilizer onto your plants, then choose a crude fertilizing system that is more “hit and miss” than anything else. Conversely if you desire an accurate system, then you may seek a dial or linear scale with fine graduations.

Venturi fertigation systems can be successful in certain applications. However, changes in water pressure, flow-rates, fertilizer density etc can significantly effect the venturi performance and accuracy, to the point that it may no longer work.

Other fertilizer systems incorporate a “dial” which has no "scale" or point of reference. These systems are meaningless and offer no assurance of fertilizer dose rate.

Some systems only have three (3) or four (4) settings - requiring you to decide if these limited dose rates suit the spread and breadth of fertilizers you intend to use.

Make note of your expected Dose Accuracy – in particular how you want to set the dose rate and the ability of the system to deal with external fluctuations.

6. Intended Fertilizer Frequency

Previously you recorded the fertilizer concentrations to be used. However, these concentrations assumed you will fertilize at the frequency nominated by the fertilizer manufacturer.

If you intend to increase fertigation frequency, then the delivered fertilizer concentration must change by either:

  • A change in the dose rate settings on the fertigation system, or
  • Dilution of the fertilizer concentration

As an example, assume a manufacturer specifies a fertilizer concentration of 25ml of fertilizer / 10L of water be applied every 10 days.

Then if you wish to fertilize every day you have two primary options:

1. Reduce fertilizer concentration by 1/10th and fertilize at a rate of 2.5mL/10L

This solution requires a very unique and specialised (expensive) fertigation system to achieve:

(25ml/10 days) / 10L = 5mL /10L or;
1 : 4000 ratio or;
2.5%

2. Dilute the fertilizer concentration 10 times and fertilize at the rate of 25ml / 10L

This is a cheaper, more practical way to accommodate daily fertilizing. Diluting the fertilizer such that 1/10th volume is fertilizer and 9/10th volume is water. Fertilize at the manufacturers recommended rate eg 25ml / 10L in this example.

Consider your intended fertilizer frequency and compare this to the remaining fertigation units to ensure they all can meet your requirements.

7. System versatility / intended use

One of the most important criteria- how do you intend to use the fertigation system and what level of flexibility you require?. Are you intending:

  • Use solely with a hand-held hose
  • Use solely with a drip irrigation system
  • Flexible - use with either hose or drip irrigation system.
  • Do you want a fixed or portable system

Consider and record your requirements.

8. Frequency you will change fertilizers / seaweed extracts

Most people use a variety of fertilizers and seaweed extracts which has a material bearing on the type of fertilizer system chosen.

Some fertigation systems use “underground” or “in-ground” tanks to store fertilizer concentrate. Whilst this keeps the tank “out of sight”, it proves a challenge when you need to empty the tank to introduce another type of fertilizer or seaweed extract.

Most fertigation systems simply require the fertilizer container be placed near the pump / tap while fertilizing. When the task is finished you return the fertilizer container to your shed. This type of system allows you to keep your garden tidy and allows for easy change between fertilizer types.

Consider the ease / difficulty certain fertigation systems will impose on you and reject those that are not acceptable.

9. How Easily and frequently do I want to replenish the fertilizer storage

Most automatic fertilizer systems allow you to easily replenish the fertilizer at will. However, systems buried in the ground may cause you concern if you need to frequently replenish the fertilizer storage tank.

If you wish to use an in-ground system, consider over sizing the storage vessel so the replenishment task becomes infrequent.

Please note “over sizing the storage vessel” will restrict your ability to easily change fertilizer types.

Consider how frequently you wish to change fertilizer types and the ease to do so.

10. Ease to check available fertilizer level.

Checking the level of remaining fertilizer could be significantly more difficult if your fertilizer tank is stored in the ground compared to being stored adjacent to the tap / faucet.

Consider the ease you would like to be able to inspect the fertilizer level, record your preference and review the fertigation systems under consideration.

11. Ability to validate system operation.

There will be occasions when you want to validate the fertilizer system is operating. Some fertigation systems allow the user to see fertilizer concentrate flowing, pumps working etc whereas others show no sign whatsoever and fertilizer movement may not even be visible.

Consider whether you are likely to want validations and reject those systems that are likely to cause you future concern.

 

We trust the above assists you to select your optimal fertigation system which will make it easy, quick and effortless to regularly fertilize your plants.

Warren Buffet famously stated “Price is what you pay, Value is what you get”. This applies to most things in life, fertigation systems included. We discuss here the value you can realise from an appropriately selected fertigation system.

 

Please do not hesitate to contact us if we can assist in any way.



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