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The General Meeting followed by the AGM was held at Peter & Meredith’s.
16 Members attended and we had 7 apologies, but we got through the business of elections.
Welcome to all the new incoming committee office holders and to the out going committee thank you all for your commitment over the many years.
To our out going President Kyra, thanks, you were a great President and will be surely missed, we all hope you and Jeff enjoy “Grey Nomading” and we will see you at a meeting when back in town.
Meredith has offered to do the Newsletter and any Advertising. Molly has kindly offered to do the Raffles and Russell is continuing on as Storeman and has offered to do the handling of our library.
Coming Events
August Meeting : Peter & Meredith’s
September Meeting : Vince’s Gourmet Lettuce Farm – North/West Gin Gin
Reminder:
1. Please bring a folding Chair.
2. Something for the raffle table.
3. One Dollar ($1) each for morning tea.
4. The host to give a talk.
Happy Birthday to any one having a Special Day in July
This Month Recipes
Burke’s Backyard Fact sheet:
Tracy Rutherford’s apple & cinnamon pancakes
This Month’s Hydroponic Information
(I know it is a bit long but thought it may be of interest Meredith)
Issue 14
Hydroponics & Greenhouses magazine
Jan/Feb - 1994
Story Title: Nutrient Management in Hydroponics Systems - Part 2
Author: Rick Donnan
Part 2 - General Principles
There have been many articles written on hydroponic nutrient
formulation and it is a topic discussed at length in most
hydroponic books. However, almost nothing has been written about
managing nutrition in hydroponic systems, which is a much more
important topic. In practice there is no such thing as a perfect
nutrient solution. Even if a nutrient feed solution is
apparently close to ideal, if not managed properly it will
eventually have nutritional problems. The first part in the
series introduced the principles involved in nutrient
management. Part 2 describes the detailed management of "closed"
systems, and "open" systems.
Water Quality
The quality of the raw water you use will
have a major impact on the type of crop you can grow, the system
you grow it in, and how you manage it. In terms of nutrient
solutions, by quality I mean the salts (ions) dissolved in the
water. This can only be found by having the water chemically
analysed. If you use town water the water authority will
normally be able to provide this for you. If you use bore, dam
or stream water, etc, you need to send a sample for analysis.
Problem Ions in Water Supplies
The most common ions in water supplies
which influence plant nutrition are:
Sodium (Na+) and Chloride (Cl-) - the
constituents of common salt. These normally occur together and
are not taken up to any degree by most plants, especially
sodium. Therefore, they tend to accumulate if present in
significant amounts. This is shown in Figure 3. Chloride is
actually a trace element (micronutrient), but is usually
available in far greater concentration than required for
nutrition. This is why it is virtually never included in
formulations.
Iron (Fe ... ). Although iron is a
micronutrient, in this form it rapidly oxidizes and precipitates
as rust, which makes it unavailable as a nutrient. In practice
this can give problems, especially by blocking drippers, so the
precipitation is best speeded up by aerating the water, followed
by settling or filtration.
Calcium (Ca++) and Magnesium (Mg++).
These are constituents in hard water. As major nutrients
(macronutrients) they are useable in the nutrient solution.
Their presence should be allowed for in calculating
formulations.
Bicarbonate (HCO3). Also a constituent in
hard water. It is not a nutrient but is alkaline and will raise
the pH. It will need to be neutralized by acid, typically
phosphoric or nitric. The amount of equivalent phosphorus or
nitrogen added should be allowed for in calculating
formulations.
Boron (B). Boron is the micronutrient
with the narrowest range. If present in the water it can be
omitted from your formulation. It can become a problem if its
concentration is over 1ppm, or lower for sensitive crops. This
only occurs in a few water supplies.
High Salt Levels in Water Supplies
The level of salts which can be tolerated
in the water depends on their composition and which crop is to
be grown. Even 50ppm of sodium can be toxic to plants such as
lettuce, strawberry and rose. In contrast tomato could cope
with over 200ppm. Because of the accumulation that will develop,
water supplies with increasing dissolved solids will make
management more critical. Beyond a certain limit, dependant upon
the crop, recirculating systems will become unmanageable. Non-recirculating
systems can continue to be used but with increased percentage
run-off. Eventually, water becomes so bad that it is unusable
in any system. In this case the only possible solution is to
remove the bulk of the salts from the water, typically with
reverse osmosis.
Water Treatment
If managed correctly reverse osmosis is
capable of reducing the dissolved salts to very low levels. The
major and most expensive component of a reversed osmosis (RO)
machine is the membrane. The efficiency and life of the membrane
is very dependant upon the water quality being pumped through
it. Often, chemical pre-treatment, such as removing iron, is
necessary for the equipment to work effectively, and to give
reasonable membrane life. The discharge system from an RO
machine is more concentrate than the input and this may be
unacceptable in some circumstances.
An alternative is to collect rainwater.
This may be used direct if sufficient is available or mixed with
the poorer water supply to make it more acceptable.
Unfortunately, in many areas of Australia, rainfall is so irregular
that when you most need fresh water is when there's none
available.
There are other contaminants in raw water
that need attention, but I will mention them only briefly.
Suspended matter should be settled out if
possible and removed. Good final filtration with a sand filter
for example, can avoid many of the dripper blockages experienced
by some growers. the water should be free of diseases
(pathogens). Town water is usually safe but other sources need
to be sterilized, most commonly by chlorinating. Water also
needs to be free of plant poisons (phytotoxins).
Fertilizers
There are a very wide range of commercial
fertilizers available and an even wider range of formulations
published. So, how do you tell which ones to use? I'm obviously
not going to recommend any individual commercial brands. What
I'll do is give some principles for guidance.
Mix Your Own, or Buy Premix?
Firstly, do you mix your own, or do you
buy a prepared fertilizer? For the beginner, especially, it is
best to buy a premix. For hobbyists, if part of the appeal of
hydroponics is mixing your own nutrient, then go ahead. The
hobbyist without this interest is probably advised to stick with
the premix. Setting up to mix your own
requires buying a moderately accurate capacity scale plus a very
accurate small scale for the micronutrient fertilizers.
For the commercial grower there are
similar choices. The grower who manages the system well, and is
getting solutions analysed regularly, should obviously mix their
own. In fact, failing to do this removes the opportunity to make
the adjustments indicated by the analysis.
However, there are growers who never have
any analysis done and have no interest in accurately weighing
fertilizers. They are probably better off buying a premix with
which they have experience and are confident about. Mixing
individual fertilizers gives a saving in direct nutrient costs,
however, there are extra labour costs involved. More
importantly, if even one serious mistake is made it can prove
more costly than any number of years savings on fertilizer.
Unfortunately, I have seen several cases of total loss of crops
through mistakes in mixing.
Types of fertilizers
For the inexperienced grower there are
several major traps to avoid. Firstly, it is essential to buy a
"hydroponic" fertilizer. Normally these would be the only types
stocked by a hydroponic retailer or wholesaler.
Unfortunately, salesmen will sometimes
promote a "complete" fertilizer as hydroponic. These are usually
soil fertilizers containing trace elements.
Unfortunately they are quite unsuitable
for hydroponics. Typically they contain little or no calcium
(Ca++) or magnesium (Mg ++); they have a very high proportion,
often 50%, of nitrogen in the ammonium (NH4+) form rather than
predominantly the nitrate (N03) form as with hydroponic
fertilizers; also they have a different balance of trace
elements.
There are other fertilizers designed for
liquid irrigation of soil crops by trickle irrigation. This is
also known as fertigation. For our purpose these fertilizers are
similar to the "complete" types, and should also be avoided.
How do you recognize these fertilizers?
Check the following: the calcium (Ca) content should be from
about the same to 30% lower than the nitrogen (N) content. The
magnesium (Mg) content should be about 20% to 30% of the calcium
content. No more than 10% of the nitrogen should be in the
ammonium (NH4) form, and none should be urea.
Occasionally growers unknowingly, or even
deliberately, use these fertilizers. The first indication of
potential problems is the pH of the run-off or recirculating
solution. Because of the high ammonium content this drops
quickly and severely, often to under pH4. With time the plant
shows obvious general symptoms of stress poor growth, and lack
of vigour.
Preparing feed solutions
There are basically two choices of ways
to mix and use the feed nutrient solution. Firstly, the solution
can be prepared at working strength, say at an EC of about
2mS/cm (milliSiemens/centimetre). This is usually done in a
suitable sized tank which is filled with water and the
fertilizer added. The solution is pumped and bypassed back to
the tank for some time in order to thoroughly mix the tank
contents.
When mixing is completed the EC and pH of
the solution should be checked and adjusted if necessary. If you
don't have a meter, then one trap to avoid is to take care to
add only enough fertilizer for the extra volume of water you
have added to the tank. Say you add sufficient fertilizer to make a full tank of
the strength you require, but the tank was not fully empty. The
actual solution strength will then be higher than you planned.
Not only that, but it gets progressively stronger each time.
This system is also used by small
commercial growers. Particularly if they expand, the choice
eventually becomes one between the cost of a new mixing system,
versus the inconvenience of frequently mixing tanks.
Concentrated food solutions
With the second method, usually installed
for convenience, concentrated fertilizers are used.
These are typically fed by injectors or
injection pumps into the water or recirculating nutrient
solution. A feedback controller is often also installed to keep
pH and EC controlled.
A complication arises when using
concentrated solutions, which are typically 100 to 200 times
stronger than the normal nutrient solutions. At this strength
calcium and most of the phosphate combine to precipitate
insoluble calcium phosphate. To a lesser extent, calcium
sulphate is also precipitated, as is iron phosphate. These
reactions are not a problem at normal feed strengths, because
these compounds are sufficiently soluble at these much weaker
strengths. As a rough analogy, it is easy to dissolve one
teaspoonful of sugar in a cup to tea, dissolving 100 teaspoons
full is impossible.
To avoid this complication the
concentrated solution so split into two parts, usually referred
to as "Part A" and "Part B". This split is to separate the
calcium and iron from the phosphate and sulphate. Therefore Part
A usually contains the calcium nitrate and iron chelate. Part B
contains all the other fertilizers. These are then injected
separately into the water flow to give a working strength
solution which is fully soluble.
It would obviously be more convenient and
halve the cost of injectors, etc, if a single concentrated mix
was possible. There have been numerous attempts to do just this,
but I don't yet know of any that have been successful. In simple
terms, there have been two basic approaches to this.
One is to use a fertigation solution, as
described in the previous section. This leads to the same
results as noted before. The other is to use a more typical
hydroponic formulation and try to keep the precipitate form
forming. I don't yet know of anyone who has done this
successfully.
This has implications for buying
nutrients in liquid form. For buying concentrated nutrient
solution I would recommend a two part product. If you want a
single part mix, check the label as suggested earlier. If it
seems to be a typical hydroponic formulation it will probably
have precipitated. It is essential to shake this product well,
immediately before pouring it into your working tank. This then
gives you some chance of getting a balanced nutrient solution.
Failure to do this will give a phosphate deficient solution,
which will result in pretty stunted purple tomato seedlings, for
example.
Nutrition in open and closed systems
Table 1. Comparison of nutrient
composition of root zone and the equivalent recirculated and
non-recirculated feed solutions.
Notes:
(a) Corrected to the same
strength for each solution for the comparison purpose.
(b) Totals for the columns only - they do
not indicate total TDS ppm.
(c) Based on "Nutrient solutions for
vegetables and flowers grown in water or substrates" 1992.
Sonneveld & Straven, Glasshouse Crops Research Station Naaidwijk.
There are two fundamental types of
soilless systems, mainly open and closed. The nutrient feed
formulations differ considerably and I discuss this here. Other
aspects of managing these systems will be covered in later
parts of this series.
In closed systems the nutrient solution
is recirculated. They may be operated either continuously as
with the Nutrient film Technique (NFT), or intermittently as
with flood and drain systems. In closed systems the nutrient
solution is recirculated. They may be operated either
continuously as with the Nutrient Film Technique (NFT), or
intermittently as with flood and drain systems. In open
systems the nutrient solution is not recirculated. Also known as
run to waste systems, they use dripper irrigation of soilless
media in containers.
Nutrition in closed systems
A simplified background to the feed
nutrition differences between these systems is as follows:
A healthy plant will take up the nutrient
balance it requires provided the solution around the roots
contains nothing at a deficient or toxic level. In a totally
closed system the only nutrient usage is what the plant takes
up. if the nutrient solution in the root zone is to remain in
balance, then what is fed in must have exactly the same balance
as the plant uptake. If not, the solution within the system gets
out of balance and continues to get further out of balance. If
this happens then solution must be discarded from the system.
The concept many find difficult to grasp
is that the solution in the system may have quiet a different
balance to the feed solution. Please refer to the Dutch
guideline figures in Table 1.
The "Root zone solution" is the same for
both recirculating and non-recirculating feeds.
Why is it different to the feed
solutions? The answer is related to the rate of uptake. For
growth rates there needs to be maximum nutrient uptake. However,
uptake is more difficult and slow for some nutrients than for
others. Increasing the strength of root zone solution for those
nutrients will increase the driving force and boost their rate
of uptake.
Fundamental Management Techniques
for all Systems
Sample regularly, preferable daily.
Sample the feed and, especially, the solution around the plant
roots (or the run-off in open systems).
Analyse all samples for pH and,
especially, EC.
Occasionally get a full chemical analysis
done. If needed this could be tied to a leaf analysis.
Record the results in a diary. Include
other information such as weather conditions, crop performance
and symptoms, pests, diseases.
Manage by watching for trends and
adjusting gently to correct them. Try to avoid taking severe
action.
Referring to Figure 1, compare the
recirculating feed solution, which is the actual plant uptake,
with the root zone solution. Calcium, magnesium and sulphur are
far higher, up to double the strength of the feed. These are
nutrients which have a slow uptake. In comparison, nitrogen is
about the same strength but potassium is lower indicating a
faster uptake. Finally, phosphate and especially, ammonium is
much lower to compensate for their very fast uptake. In fact
ammonium uptake is so fast that its concentration may well drop
to almost zero.
The intended balance in the root zone may
be built up gradually or it may be done by having a special
starter solution. Starter solutions will obviously be higher
than normal in calcium, magnesium and sulphur.
Nutrition in open systems
With the non-recirculated feed there is
not only plant uptake, but run-off as well. The feed is
therefore part way between supplying the uptake and providing
the required root zone solution strength. By the time it runs off
it has built up to the required balance in the medium.
If an adequate run-off is maintained
then any imbalance goes out with it. For this reason the feed
composition is nowhere near as vital as with the recirculating
system. Therefore, nutrient management is far easier in a non-
recirculating system. This is a major reason why until the present over 90% of the worlds hydroponics systems are open type systems.
This Month’s jokes
IT'S NOT TRUE THAT ONLY A "DOG PERSON" WOULD TRULY APPRECIATES THIS!
STAY
I pulled into the crowded parking lot at the local shopping center and rolled down the car windows to make sure my Labrador Retriever Pup had fresh air.
She was stretched full-out on the back seat and I wanted to impress upon her that she must remain there.
I walked to the curb backward, pointing my finger at the car and saying emphatically,
"Now you stay. Do you hear me?"
"Stay! Stay!"
The driver of a nearby car, a pretty blonde young lady, gave me a strange look and said,
"Why don't you just put it in Park?"
Poetry
OLD POETS RHYME
By Mavis Appleyard, Warren, NSW.
It really seems to be our fate
To find we have a used by date
That is when our bodies find
Our performance is just in our mind.
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